March 31, 1882.] 



KNOWLEDGE * 



465 



disproving this idea rests with those who deny evolution. 

 Until we receive a fuller and more likely explanation 

 of such likenesses as those we are at present discussing, 

 ■we are entitled to hold to the only theory, which, so far 

 as I know, satislics the requirements of a good hypothesis — 

 these requirements being that it explains all the facts and 

 is contrary to none. This end the theory of evolution 

 attains in explaining both the likenesses and the dissimi- 

 larities of li\ing nature. 



Returning, after this needful digression, to the case of 

 birds and reptiles, let us firstly note the structural points 

 in which these classes agree. To begin with, the skull of 

 both is joined to the spine by one bony process or condyle. 

 There are two of these processes in frogs and their neigh- 

 bours, and a similar number in quadrupeds, including man. 

 Then, secondly, the lower jaw of a reptile agrees with that 

 of a bird in its compound nature. This jaw, instead of being 

 simple and composed of two simple halves (as in quadru- 

 peds), consists in birds and reptiles of from eight to twelve 

 distinct pieces, which are amalgamated to form one bone. 

 Furthermore, whilst the quadruped's lower jaw is joined 

 directly, and of itself, to the skuU, that of the bird and i-eptile 

 is attached to the skull through the medium of a distinct 

 bone, which is named the quadrate hone. Curiously 

 enough, this bone in the quadruped is pushed upwards into 

 the middle of the skull in the course of development, and 

 becomes one of the three small bones (malleus) of the 

 internal ear. Again, reptiles and birds agree in possessing 

 lungs alone as their breathing organs. No gills are 

 developed (as in frogs and fishes) at any period of 

 reptile or bird-life, although both, like quadrupeds, possess 

 gill-clefts in the neck in early life. These " gill-clefts," seen 

 in the early life of man himself, are to be viewed as feeble 

 survivals of the aquatic ancestry from which, according to 

 evolution, all Vertebrate animals have sprung. Further- 

 more, instead of the ankle-joint (as in man and quadrupeds) 

 being situated between the end of the leg, so to speak, and 

 the beginning of the ankle-bones, this joint in reptiles and 

 birds exists in the middle of the ankle-bones themselves. 

 This curious feature will be further alluded to later on. 



The technical naturalist would enumerate other points of 

 agreement between birds and reptiles, but sutiicient has 

 been said to show the close affinities which lie just beneath 

 the surface of their organisation. Their differences, how- 

 ever, are also of pronounced type. The causes to which in 

 the far-back past the evolutionist conceives the likeness 

 between these animals to be due, have operated, through 

 variation, at a less remote period, to produce the divergent 

 lines of development." Thus we discover that birds are 

 warm-blooded, whilst reptiles possess cold blood ; the 

 bird's feathers are unknown in the reptile-world ; and 

 the perfect heart and circulation of the bird — similar 

 to that of man — are also unrepresented in reptiles. 

 Crocodiles, which possess a four-chambered heart, like 

 birds and quadrupeds, nevertheless exhibit the same 

 imperfect and " mixed " circulation seen equally in 

 frogs and reptiles. The lungs of birds are of "open" 

 structure, and part of the air inspired passes through the 

 lungs to fill certain " air sacs " in the bird's body, and also 

 fills the interior of the bones in most birds. Such a dis- 

 tribution of air in the bird's body is evidently adapted for 

 the exigencies of flight. On the whole, then, with certain 

 well-marked likenesses — which, be it observed, evolution 

 accounts for on the idea of a common origin — the classes of 

 birds and reptiles are demarcated from one another by 

 cei-tain highly-distinctive characters. 



The dissimilarities on the hypothesis of evolution are 

 due to variation and modification ; but, if this idea be 

 correct, can we show the stages through which the varia- 



tion has led these two groups 1 In other words, have the 

 " links " which should hypothetically connect them, any 

 existence whatever ? Such an inquiry would have been 

 answered in the negati\e only a few years ago ; but, thanks 

 to recent research, wo are now enabled, satisfactorily 

 enough, to bridge the gulf between birds and reptiles, 

 and in a measure to reconstruct the pedigree of these 

 curious races. 



To render my remarks clear, it may be well at this stage 

 to show in a tabular form the relative positions of the rock- 

 formations with which we shall have to deal. Placed in 

 the order in which they occur in the earth's crust, the 

 rocks in question lie thus : — 



^ Recent. 

 Tertiary j Pliocene. 

 Hocks. J Miocene. 

 C Eocene. 



„ , r Chalk. 

 Secondary I y^,.j^_ 



^"'■'''- [Trias. 



The meaning of this table becomes clear, if it be borne 

 in mind that the rocks as here noted are divided into the 

 older Secondaries and the newer Tertiaries. The Eocene in 

 turn is the oldest (or lowest) series of the Tertiary rocks, 

 as the Trias is the oldest of the Secondary rocks. 



The fossil remains of birds are few and far between, and 

 this for the reason pointed out by Lyell — namely, that the 

 body of a bird falling into water, prior to its entombment 

 in the deposits which form the rocks of the future, would 

 float, and would aflbrd a likely object of prey to other 

 animals ; thus escaping the chances of preservation. For 

 long, fossil birds were regarded as limited to the Tertiary 

 rocks ; but we now know of their existence in the Chalk, or 

 Cretaceous Period ; and we have also obtained fossil speci- 

 mens from the rocks immediately preceding the Chalk in 

 time, namely the Oolitic or Jurassic Period. 



It is almost needless to remark that the bird-remains of 

 the Tertiary rocks, as a rule, resemble closely the birds of 

 our own day. In this light they only testify to the age of 

 some of our existing groups of birds, and do not directly sup- 

 port the theory of evolution, whilst, of course, they do not in 

 any way negative it. But in tlie deposits of the London clay 

 of Sheppey, belonging to the Eocene (Tertiary) period of 

 geology, tiie remains of a bird, belonging apparently to the 

 swimmers, were discovered. This form was named Odon- 

 toptcryx by Professor Owen, and its remarkable jaw- 

 armature at once attracted the notice of naturalists. 

 No existing bird has teeth ; and no bird possesses any 

 structures approaching teeth in function — save, perhaps, 

 such birds as the Mergansers, in which the horny 

 margin of the jaw is cut into a series of projections, 

 adapted for retaining a secure hold of the finny prey on 

 which these birds subsist. But in the Odontopteryx, the 

 jaws were beset with strong bony processes, which, though 

 resembling teeth in appearance, nevertheless are mere pro- 

 jections of bone — for, as most readers know, teeth are not 

 of bony nature, but possess a special and distinct structure 

 of their own. Nevertheless, the fact of this extinct bird 

 of the Eocene rocks possessing toothed projections of its 

 jaws, serves to link it, in the opinion of naturalists, to the 

 reptile hosts : for teeth are as stable and characteristic 

 possessions of the reptile class as their absence is a natural 

 feature of existing birds. 



{To he continued.) 



The Sound, or Swim-bladdek of Fish. — Erratum. In my letter 

 (Knowledge, Marcli 17, p. 439), for " a swimming paii-," read " a 

 swimming pow " ; for " straight," read " strait."— W. Houghton. 



