We are met, unfortunately, at the outset by one of those curious obstacles to inquiry which have so often barred the way of truth and turned discovery into ridicule. It happens that the class of animals in which Science, in the very nature of the case, is compelled to look for the closest affinities to human beings is that of the Apes. This simple circumstance has told almost fatally against the wide acceptance of the theory of Descent. There is just as much truth in the sarcasm that man is a "reformed monkey" as to prejudge the question to the unscientific mind. But the statement is no nearer the truth itself than if one were to say that a gun is an adult form of the pistol. The connection, if any, between Man and Ape is simply that the most Man-like thing in creation is the Ape, and that, in his Ascent, Man probably passed through a stage when he more nearly resembled the Ape than any other known animal. Apart from that accident, Evolution owes no more to the Ape than to any other creature. Man and Ape are alike in being two of the latest terms of an infinite series, each member of which has had a share in making up the genealogical tree. To single out the Ape, therefore, and use the hypothetical relationship for rhetorical purposes is, to say the least, unscientific. It is certainly the fact that Man is not descended from any existing ape. The anthropoid apes branched off laterally at a vastly remote period from the nearest human progenitors. The challenge even to produce links between Man and the living man-like apes is difficult to take seriously. Should anyone so violate the first principles of Evolution as to make it, it is only to be said that it cannot be met. For an anthropoid ape could as little develop into a Man as could a Man pass backwards into an anthropoid ape. References to a Simian stem play no necessary part in the story of the Ascent of Man. In those pages the compromising name will scarcely occur. If historical sequence compels us to make an apparent exception here at the very outset, it will be seen that the allusion is harmless. For the analogy we are about to make might with equal relevancy have been drawn from a squirrel or a sloth.
On the theory that human beings were once allied in habit as well as in body with some of the apes, that they probably lived in trees, and that baby-men clung to their climbing mothers as baby-monkeys do to-day, Dr. Louis Robinson prophesied that a baby's power of grip might be found to be comparable in strength to that of a young monkey at the same period of development. Having special facilities for such an investigation, he tested a large number of just-born infants with reference to this particular. Now although most people have some time or other been seized in the awful grasp of a baby, few have any idea of the abnormal power locked up in the tentacles of this human octopus. Dr. Robinson's method was to extend to infants, generally of one hour old, his finger, or a walking stick, to imitate the branch of a tree, and see how long they would hang there without, what the newspapers call, "any other visible means of support." The results are startling. Dr. Robinson has records of upwards of sixty cases in which the children were under a month old, and in at least half of these the experiment was tried within an hour of birth: "In every instance, with only two exceptions, the child was able to hang on to the finger or a small stick, three-quarters of an inch in diameter, by its hands, like an acrobat from a horizontal bar, and sustain the whole weight of its body for at least ten seconds. In twelve cases, in infants under an hour old, half a minute passed before the grasp relaxed, and in three or four nearly a minute. When about four days old, I found that the strength had increased, and that nearly all, when tried at this age, could sustain their weight for half a minute. About a fortnight or three weeks after birth the faculty appeared to have attained its maximum, for several at this period succeeded in hanging for over a minute and a half, two for just over two minutes, and one infant of three weeks old for two minutes thirty-five seconds. . . . In one instance, in which the performer had less than one hour's experience of life, he hung by both hands to my forefinger for ten seconds, and then deliberately let go with his right hand (as if to seek a better hold), and maintained his position for five seconds more by the left hand only. Invariably the thighs are bent nearly at right angles to the body, and in no case did the lower limbs hang down and take the attitude of the erect position. This attitude, and the disproportionately large development of the arms compared with the legs, give the photographs a striking resemblance to a well-known picture of the celebrated Chimpanzee Sally at the Zoological Garden. I think it will be acknowledged that the remarkable strength shown in the flexor muscle of the fore-arm in these young infants, especially when compared with the flaccid and feeble state of the muscular system generally, is a sufficiently striking phenomenon to provoke inquiry as to its cause and origin. The fact that a three-week-old baby can perform a feat of muscular strength that would tax the powers of many a healthy adult is enough to set one wondering. A curious point is that in many cases no sign of distress is evident, and no cry uttered until the grasp begins to give way." 
Place side by side with this the following account, which Mr. Wallace gives us in his Malay Archipelago of a baby Orang-outang, whose mother he happened to shoot:
"This little creature was only about a foot long, and had evidently been hanging to its mother when she first fell. Luckily it did not appear to have been wounded, and after we had cleaned the mud out of its mouth it began to cry out, and seemed quite strong and active. While carrying it home it got its hands in my beard, and grasped so tightly that I had great difficulty in getting free, for the fingers are habitually bent inward at the last joint so as to form complete hooks. For the first few days it clung desperately with all four hands to whatever it could lay hold of, and I had to be careful to keep my beard out of its way, as its fingers clutched hold of hair more tenaciously than anything else, and it was impossible to free myself without assistance. When restless, it would struggle about with its hands up in the air trying to find something to take hold of, and when it had got a bit of stick or rag in two or three of its hands, seemed quite happy. For want of something else, it would often seize its own feet, and after a time it would constantly cross its arms and grasp with each hand the long hair that grew just below the opposite shoulder. The great tenacity of its grasp soon diminished, and I was obliged to invent some means to give it exercise and strengthen its limbs. For this purpose I made a short ladder of three or four rounds, on which I put it to hang for a quarter of an hour at a time. At first it seemed much pleased, but it could not get all four hands in a comfortable position, and, after changing about several times, would leave hold of one hand after the other and drop on to the floor. Sometimes when hanging only by two hands, it would loose one, and cross it to the opposite shoulder, grasping its own hair; and, as this seemed much more agreeable than the stick, it would then loose the other and tumble down, when it would cross both and lie on its back quite contentedly, never seeming to be hurt by its numerous tumbles. Finding it so fond of hair, I endeavoured to make an artificial mother, by wrapping up a piece of buffalo-skin into a bundle, and suspending it about a foot from the floor. At first this seemed to suit it admirably, as it could sprawl its legs about and always find some hair, which it grasped with the greatest tenacity" 
Whatever the value of these facts as evidence, they form an interesting if slight introduction to the part of the subject that lies before us. For we have now to explore the Body itself for actual betrayals -- not mere external movements which might have come as well from early Man as from later animal; but veritable physical survivals, the material scaffolding itself -- of the animal past. And the facts here are as numerous and as easily grasped as they are authentic. As the traveller, wandering in foreign lands, brings back all manner of curios to remind him where he has been -- clubs and spears, clothes and pottery, which represent the ways of life of those whom he has met -- so the body of Man, emerging from its age-long journey through the animal kingdom, appears laden with the spoils of its distant pilgrimage. These relics are not mere curiosities; they are as real as the clubs and spears, the clothes and pottery. Like them, they were once a part of life's vicissitude; they represent organs which have been outgrown; old forms of apparatus long since exchanged for better, yet somehow not yet destroyed by the hand of time. The physical body of Man, so great is the number of these relics, is an old curiosity shop, a museum of obsolete anatomies, discarded tools, outgrown and aborted organs. All other animals also contain among their useful organs a proportion which are long past their work; and so significant are these rudiments of a former state of things, that anatomists have often expressed their willingness to stake the theory of Evolution upon their presence alone.
Prominent among these vestigial structures, as they are called, are those which smack of the sea. If Embryology is any guide to the past, nothing is more certain than that the ancient progenitors of Man once lived an aquatic life. At one time there was nothing else in the world but water-life; all the land animals are late inventions. One reason why animals began in the water is that it is easier to live in the water -- anatomically and physiologically cheaper -- than to live on the land. The denser element supports the body better, demanding a less supply of muscle and bone; and the perpetual motion of the sea brings the food to the animal, making it unnecessary for the animal to move to the food. This and other correlated circumstances call for far less mechanism in the body, and, as a matter of fact, all the simplest forms of life at the present day are inhabitants of the water.
A successful attempt at coming ashore may be seen in the common worm. The worm is still so unacclimatized to land life that instead of living on the earth like other creatures, it lives in it, as if it were a thicker water, and always where there is enough moisture to keep up the traditions of its past. Probably it took to the shore originally by exchanging first the water for the ooze at the bottom, then by wriggling among muddy flats when the tide was out, and finally, as the struggle for life grew keen, it pushed further and further inland, continuing its migration so long as dampness was to be found.
More striking examples are found among the molluscs, the sea-faring animals par excellence of the past. A snail wandering over the earth with a sea-shell on its back is one of the most anomalous sights in nature -- as preposterous as the spectacle of a Red Indian perambulating Paris with a birch canoe on his head. The snail not only carries this relic of the sea everywhere with it, but when it cannot get moisture to remind it of its ancient habitat, it actually manufactures it. That the creature itself has discovered the anomaly of its shell is obvious, for in almost every class its state of dilapidation betrays that its up-keep is no longer an object of much importance. In nearly every species the stony houses have already lost their doors, and most have their shells so reduced in size that not half of the body can get in. The degeneration in their cousins, the slugs, is even more pathetic. All that remains of the ancestral home in the highest ranks is a limpet-like cap on the tip of the tail; the lowest are sans everything; and in the intermediate forms the former glory is ironically suggested by a few grains of sand or a tiny shield so buried beneath the skin that only the naturalist's eye can see it.
When Man left the water, however -- or what was to develop into Man -- he took very much more ashore with him than a shell. Instead of crawling ashore at the worm stage, he remained in the water until he evolved into something like a fish; so that when, after an amphibian interlude, he finally left it, many "ancient and fish-like" characters remained in his body to tell the tale. The chief characteristic of a fish is its apparatus for breathing the air dissolved in the water. This consists of gills -- delicate curtains hung on strong arches and dyed scarlet with the blood which continually courses through them. In many fishes these arches are five or seven in number, and communicating with them -- in order to allow the aerated water, which has been taken in at the mouth, to pass out again after bathing the gills -- an equal number of slits or openings is provided in the neck. Sometimes the slits are bare and open so that they are easily seen on the fish's neck -- anyone who looks at a shark will see them -- but in modern forms they are generally covered by the operculum or lid. Without these holes in their neck all fishes would instantly perish, and we may be sure Nature took exceptional care in perfecting this particular piece of the mechanism.
Now it is one of the most extraordinary facts in natural history that these slits in the fish's neck are still represented in the neck of Man. Almost the most prominent feature, indeed, after the head, in every mammalian embryo, are the four clefts or furrows of the old gill-slits. They are still known in Embryology by the old name -- gill-slits -- and so persistent are these characters that children are known to have been born with them not only externally visible which is a common occurrence but open through and through, so that fluids taken in at the mouth could pass through and trickle out at the neck. This last fact was so astounding as to be for a long time denied. It was thought that, when this happened, the orifice must have been accidentally made by the probe of the surgeon. But Dr. Sutton has recently met with actual cases where this has occurred. "I have seen milk," he says, "issue from such fistulae in individuals who have never been submitted to sounding."  In the common case of children born with these vestiges, the old gill-slits are represented by small openings in the skin on the sides of the neck, and capable of admitting a thin probe. Sometimes even the place where they have been in childhood is marked throughout life by small round patches of white skin.
Almost more astonishing than the fact of their persistence is the use to which Nature afterwards put them. When the fish came ashore, its water-breathing apparatus was no longer of any use to it. At first it had to keep it on, for it took a long time to perfect the air-breathing apparatus destined to replace it. But when this was ready the problem arose, What was to be done with the earlier organ? Nature is exceedingly economical, and could not throw all this mechanism away. In fact, Nature almost never parts with any structure she has once made. What she does is to change it into something else. Conversely, Nature seldom makes anything new; her method of creation is to adapt something old. Now, when Nature had done with the old breathing-apparatus, she proceeded to adapt it for a new and important purpose. She saw that if water could pass through a hole in the neck, air could pass through likewise. But it was no longer necessary that air should pass through for purposes of breathing, for that was already provided for by the mouth. Was there any other purpose for which it was desirable that air should enter the body? There was, and a very subtle one. For hearing. Sound is the result of a wave-motion conducted by many things, but in a special way by air. To leave holes in the head was to let sound into the head. The mouth might have done for this, but the mouth had enough to do as it was, and, moreover, it must often be shut. In the old days, certainly, sound was conveyed to fishes in a dull way without any definite opening. But animals which live in water do not seem to use hearing much, and the sound-waves in fishes are simply conveyed through the walls of the head to the internal ear without any definite mechanism. But as soon as land-life began, owing to the changed medium through which sound-waves must now be propagated, and the new uses for sound itself, a more delicate instrument was required. And hence one of the first things attended to as the evolution went on was the construction and improvement of the ear. And this seems to have been mainly effected by a series of remarkable developments of one of the now superfluous gill-slits.
It has long been a growing certainty to Comparative Anatomy that the external and middle ear in Man are simply a development, an improved edition, of the first gill-cleft and its surrounding parts. The tympano-Eustachian passage is the homologue or counterpart of the spiracle associated in the shark with the first gill-opening. Prof. His of Leipsic has worked out the whole development in minute detail, and conclusively demonstrated the mode of origin of the external ear from the coalescence of six rounded tubercles surrounding the first branchial cleft at an early period of embryonic life. 
Now, bearing in mind this theory of the origin of ears, an extraordinary corroboration confronts us. Ears are actually sometimes found bursting out in human beings half-way down the neck, in the exact position -- namely, along the line of the anterior border of the sterno-mastoid muscle -- which the gill-slits would occupy if they still persisted. In some human families, where the tendency to retain these special structures is strong, one member sometimes illustrates the abnormality by possessing the clefts alone, another has a cervical-ear, while a third has both a cleft and a neck-ear -- all these, of course, in addition to the ordinary ears. This cervical auricle has all the characters of the ordinary ear, "it contains yellow elastic cartilage, is skin-covered, and has muscle-fibre attached to it."  Dr Sutton calls attention to the fact that on ancient statues of fauns and satyrs cervical auricles are sometimes found, and he figures the head of a satyr from the British Museum, carved long before the days of anatomy, where a sessile ear on the neck is quite distinct. A still better illustration may be seen in the Art Museum at Boston on a full-sized cast of a faun, belonging to the later Greek period; and there are other examples in the same building. One interest of these neck-ears in statues is that they are not, as a rule, modelled after the human ear, but taken from the cervical-ear of the goat, from which the general idea of the faun was derived. This shows that neck-ears were common on the goats of that period -- as they are on goats to this day. The occurrence of neck-ears in goats is no more than one would expect. Indeed, one would look for them not only in goats and in Man, but in all the Mammalia, for so far as their bodies are concerned all the higher animals are near relations. Observations on vestigial structures in animals are sadly wanting; but these cervical-ears are also certainly found in the horse, pig, sheep, and others.
That the human ear was not always the squat and degenerate instrument it is at present may be seen by a critical glance at its structure. Mr. Darwin records how a celebrated sculptor called his attention to a little peculiarity in the external ear, which he had often noticed both in men and women. "The peculiarity consists in a little blunt point, projecting from the inwardly folded margin or helix. When present, it is developed at birth, and, according to Professor Ludwig Meyer, more frequently in man than in woman. The helix obviously consists of the extreme margin of the ear folded inwards; and the folding appears to be in some manner connected with the whole external ear being permanently pressed backwards. In many monkeys who do not stand high in the order, as baboons and some species of macacus, the upper portion of the ear is slightly pointed, and the margin is not at all folded inwards; but if the margin were to be thus folded, a slight point would necessarily project towards the centre."  Here then, in this discovery of the lost tip of the ancestral ear, is further and visible advertisement of Man's Descent, a surviving symbol of the stirring times and dangerous days of his animal youth. It is difficult to imagine any other theory than that of Descent which could account for all these facts. That Evolution should leave such clues lying about is at least an instance of its candour.
But this does not exhaust the betrayals of this most confiding organ. If we turn from the outward ear to the muscular apparatus for working it, fresh traces of its animal career are brought to light. The erection of the ear, in order to catch sound better, is a power possessed by almost all mammals, and the attached muscles are large and greatly developed in all but domesticated forms. This same apparatus, though he makes no use of it whatever, is still attached to the ears of Man. It is so long since he relied on the warnings of hearing, that by a well-known law, the muscles have fallen into disuse and atrophied. In many cases, however, the power of twitching the ear is not wholly lost, and every school-boy can point to some one in his class who retains the capacity, and is apt to revive it in irrelevant circumstances.
One might run over all the other organs of the human body and show their affinities with animal structures and an animal past. The twitching of the ear, for instance, suggests another obsolete, or obsolescent power -- the power, or rather the set of powers, for twitching the skin, especially the skin of the scalp and forehead by which we raise the eyebrows. Subcutaneous muscles for shaking off flies from the skin, or for erecting the hair of the scalp, are common among quadrupeds, and these are represented in the human subject by the still functioning muscles of the forehead, and occasionally of the head itself. Everyone has met persons who possess the power of moving the whole scalp to and fro, and the muscular apparatus for effecting it is identical with what is normally found in some of the Quadrumana.
Another typical vestigial structure is the plica semi-lunaris, the remnant of the nictitating membrane characteristic of nearly the whole vertebrate sub-kingdom. This membrane is a semi-transparent curtain which can be drawn rapidly across the external surface of the eye for the purpose of sweeping it clean. In birds it is extremely common, but it also exists in fish, mammals, and all the other vertebrates. Where it is not found of any functional value it is almost always represented by vestiges of some kind. In Man all that is left of it is a little piece of the curtain draped at the side of the eye.
Passing from the head to the other extremity of the body one comes upon a somewhat unexpected but very pronounced characteristic -- the relic of the tail, and not only of the tail, but of muscles for wagging it. Everyone who first sees a human skeleton is amazed at this discovery. At the end of the vertebral column, curling faintly outward in suggestive fashion, are three, four, and occasionally five vertebrae forming the coccyx, a true rudimentary tail. In the adult this is always concealed beneath the skin, but in the embryo, both in Man and ape, at an early stage it is much longer than the limbs. What is decisive as to its true nature, however, is that even in the embryo of Man the muscles for wagging it are still found. In the grown-up human being these muscles are represented by bands of fibrous tissue, but cases are known where the actual muscles persist through life. That a distinct external tail should not still be found in Man may seem disappointing to the evolutionist. But the want of a tail argues more for the theory of Evolution than its presence would have done. For all the anthropoids most allied to Man have long since also parted with theirs.
With regard to the presence of Hair on the body, and its disposition and direction, some curious facts may be noticed. No one, until Evolution supplied the impulse to a fresh study of the commonplace, thought it worth while to study such trifles as the presence of hair on the fingers and hands, and the slope of the hair on the arms. But now that attention is called to it, every detail is seen to be full of meaning. In all men the rudimentary hair on the arm, from the wrist to the elbow, points one way, from the elbow to the shoulder it points the opposite way. In the first case it points upwards from the wrist towards the elbow, in the other downwards from the shoulder to the elbow. This occurs nowhere else in the animal kingdom, except among the anthropoid apes and a few American monkeys, and has to do with the arboreal habit. As Mr. Romanes, who has pointed this out, explains it, "When sitting on trees, the Orang, as observed by Wallace, places its hands above its head with its elbows pointing downwards; the disposition of hair on the arms and fore-arms then has the effect of thatch in turning the rain. Again, I find that in all species of apes, monkeys, and baboons which I have examined (and they have been numerous), the hair on the back of the hands and feet is continued as far as the first row of phalanges; but becomes scanty, or disappears altogether, on the second row. I also find that the same peculiarity occurs in man. We have all rudimentary hair on the first row of phalanges, both of hands and feet, when present at all, it is more scanty on the second row: and in no case have I been able to find any on the terminal row. In all cases those peculiarities are congenital, and the total absence or partial presence of hair on the second phalanges is constant in different species of Quadrumana. . . . The downward direction of the hair on the backs of the hands is exactly the same in man as it is in all the anthropoid apes. Again, with regard to hair, Darwin notices that occasionally there appear in man a few hairs in the eyebrows much longer than the others; and that they seem to be a representation of similarly long and scattered hairs which occur in the chimpanzee, macacus, and baboon. Lastly, about the sixth month the human foetus is often thickly covered with somewhat long dark hair over the entire body, except the soles of the feet and palms of the hands, which are likewise bare in all quadrumanous animals. This covering, which is called the lanugo, and sometimes extends even to the whole forehead, ears, and face, is shed before birth. So that it appears to be useless for any purpose other than that of emphatically declaring man a child of the monkey."  The uselessness of these relics, apart from the remarkable and detailed nature of the homologies just brought out, is a circumstance very hard to get over on any other hypothesis than that of Descent.
Caution, of course, is required in deciding as to the inutility of any character, since its seeming uselessness may only mean that we do not know its use. But there are undoubtedly cases where we know that certain vestigial structures are not only useless to Man but worse than useless. Coming under this category is perhaps the most striking of all the vestigial organs, that of the Vermiform Appendix of the Caecum. Here is a structure which is not only of no use to man now, but is a veritable death-trap. In herbivorous animals this "blind-tube" is very large -- longer in some cases than the body itself -- and of great use in digestion, but in Man it is shrunken into the merest rudiment, while in the Orang-outang: it is only a little larger. In the human subject, owing to its diminutive size, it can be of no use whatever, while it forms an easy receptacle for the lodgment of foreign bodies, such as fruit-stones, which set up inflammation, and in various ways cause death. In man this tube is the same in structure as the rest of the intestine; it is "covered with peritoneum, possesses a muscular coat, and is lined with mucous membrane. In the early embryo it is equal in calibre to the rest of the bowel, but at a certain date it ceases to grow pari passu with it, and at the time of birth appears as a thin tubular appendix to the caecum. In the newly-born child it is often absolutely as long as in the full-grown man. This precocity is always an indication that the part was of great importance to the ancestors of the human species." 
So important is the key of Evolution to the modern pathologist that in cases of malformation his first resort is always to seek an explanation in earlier forms of life. It is found that conditions which are pathological in one animal are natural in others of a lower species. When any eccentricity appears in a human body the anatomist no longer sets it down as a freak of Nature. He proceeds to match it lower down. Mr. Darwin mentions a case of a man who, in his foot alone, had no less than seven abnormal muscles. Each of these was found among the muscles of lower animals. Take, again, a common case of
But the enumeration becomes tedious. Though we are only at the beginning of the list, sufficient has been said to mark the interest of this part of the subject, and the redundancy of the proof. In the human body alone, there are at least seventy of these vestigial structures. Take away the theory that Man has evolved from a lower animal condition, and there is no explanation whatever of any one of these phenomena. With such facts before us, it is mocking human intelligence to assure us that Man has not some connection with the rest of the animal creation, or that the processes of his development stand unrelated to the other ways of Nature. To say that Providence, in making a new being, should deliberately have inserted these eccentricities, without their having any real connection with the things they so well imitate, or any working relation to the rest of his body, is, with our present knowledge, simple irreverence.
Were it the present object to complete a proof of the descent of Man, one might go on to select from other departments of science evidence not less striking than that from vestigial structures. From the side of palaeontology it might be shown that Man appears in the earth's crust like any other fossil, and in the exact place where science would expect to find him. When born, he is ushered into life like any other animal; he is subject to the same diseases; he yields to the same treatment. When fully grown there is almost nothing in his anatomy to distinguish him from his nearest allies among other animals -- almost bone for bone, nerve for nerve, muscle for muscle he is the same. There is in fact a body of evidence now before science for the animal origin of Man's physical frame which it is impossible for a thinking mind to resist. Up to this point two only out of the many conspiring lines of testimony have been drawn upon for their contribution; but enough has been said to encourage us, with this as at least a working theory, to continue the journey. It is the Ascent of Man that concerns us and not the Descent. And these amazing facts about the past are cited for a larger purpose than to produce conviction on a point which, after all, is of importance only in its higher implications.
 Nineteenth Century, November, 1891.  Malay Archipelago, 53-5.  Evolution and Disease, p. 81.  Haeckel has given an earlier account of the process in the following words:--"All the essential parts of the middle ear--the tympanic membrane, tympanic cavity, and Eustachian tube--develop from the first gill-opening with its surrounding parts, which in the Primitive Fishes (Selachii) remains throughout life as an open blow-hole, situated between the first and second gill-arches. In the embryos of higher Vertebrates it closes in the centre, the point of concrescence forming the tympanic membrane. The remaining outer part of the first gill-opening is the rudiment of the outer ear-canal. From the inner part originates the tympanic cavity, and further inward, the Eustachian tube. In connection with these, the three bonelets of the ear develop from the first two gill-arches; the hammer and anvil from the first, and the stirrup from the upper end of the second gill-arch. Finally, as regards the external ear, the ear-shell (concha auris), and the outer ear canal, leading from the shell to the tympanic membrane-- these parts develop in the simplest way from the skin-covering which borders the outer orifice of the first gill-opening. At this point the ear-shell rises in the form of a circular fold of skin, in which cartilage and muscles afterwards form." --Haeckel, Evolution of Man, Vol. II., p. 269.  Sutton, Evolution and Disease, p. 87.  Descent of Man, p. 15.  Darwin and After Darwin, pp. 89-92.  Sutton, Evolution and Disease, p. 65.  Weismann, Biological Memoirs, p. 255.
 Malay Archipelago, 53-5.
 Evolution and Disease, p. 81.
 Haeckel has given an earlier account of the process in the following words:--"All the essential parts of the middle ear--the tympanic membrane, tympanic cavity, and Eustachian tube--develop from the first gill-opening with its surrounding parts, which in the Primitive Fishes (Selachii) remains throughout life as an open blow-hole, situated between the first and second gill-arches. In the embryos of higher Vertebrates it closes in the centre, the point of concrescence forming the tympanic membrane. The remaining outer part of the first gill-opening is the rudiment of the outer ear-canal. From the inner part originates the tympanic cavity, and further inward, the Eustachian tube. In connection with these, the three bonelets of the ear develop from the first two gill-arches; the hammer and anvil from the first, and the stirrup from the upper end of the second gill-arch. Finally, as regards the external ear, the ear-shell (concha auris), and the outer ear canal, leading from the shell to the tympanic membrane-- these parts develop in the simplest way from the skin-covering which borders the outer orifice of the first gill-opening. At this point the ear-shell rises in the form of a circular fold of skin, in which cartilage and muscles afterwards form." --Haeckel, Evolution of Man, Vol. II., p. 269.
 Sutton, Evolution and Disease, p. 87.
 Descent of Man, p. 15.
 Darwin and After Darwin, pp. 89-92.
 Sutton, Evolution and Disease, p. 65.
 Weismann, Biological Memoirs, p. 255.