REPTILES. 



tliat they are not covered, either by a branchial opercuhim, 

 or by radiated bones. 



The branchix, or gills, properly fo called, that is, the 

 immediate organ in which the pulmonary vedels are didri- 

 buted, are i'mall tufts formed lilce feathers, that is to fay, 

 fringed on the two fides. Each cartilaginous arc fupports 

 about thirty fuch ; and in the middle of each tuft are its 

 two principal vedels derived from the two great blood-veffels 

 of the arc. 



It may be obfcrved here, tiiat the fifiies called fyngnathi 

 have alfo their branchiae in the form of tufts. 



The heart, placed in front of this apparatus, and re- 

 ceiving the blood from the body by the vena cava, which 

 comes, as in mod cafes, in great part through the liver, has 

 only one auricle and ventricle, as in fifhes, and in adult frogs 

 and falamanders, without any of thofe divifions which are 

 obfervcd in the cheloiiian and fanrian orders. The ventricle 



fives origin to a fiiiglc artery, which is completely diltri- 

 uted on the eight branchice, fo that no drop of blood can 

 go to the reft of the body, without having paftcd through 

 tlic refpiratory organs. All the blood which has circu- 

 lated through the gills, is collefted in the branchial veins, 

 which go towards the back, and are united into a fingle 

 trunk, which becomes the defcending artery : but, before 

 uniting, they furnifh arteries to the head, fore feet, lung, 

 and liver ; fo that in the tadpole, the lung receives blood 

 which has been already expofed to the aftion of water ; 

 and this fraall portion of the animal's blood undergoes 

 reipiration twice, while, with refpeft to the great mafs of 

 the fluid, there is only one refpiration, and that of an 

 aquatic nature, or fimilar to the refpiration of fifhes. 



Great changes take place when the tadpole becomes a 

 frog ; but they are produced by very fimple means. As the 

 arms and head increafe in fize, their arteries are enlarged ; 

 the branchiae, on the contrary, are obliterated, and their 

 arteries are gradually reduced : but, as it is always necef- 

 fary that blood fhould go to the head and other parts, 

 one of the four principal branchial arteries on each fide is 

 enlarged, and ferves to convey it. Then the artery, which 

 goes out of the heart, and was formerly divided into eight 

 branches, is now fimply bifurcated, and its tvi^o branches 

 fupply the ai'terial trunks of the head, arms, lungs, &c. ; 

 and laftly, are united to form the defcending aorta. Now 

 this is precifely the circulation of the frog, in order to 

 produce which it has been merely necefiary to obUterate fix 

 of the branchial arteries of the tadpole, and to enlarge the 

 two others. Henceforward the lungs are the exclufive feat 

 of refpiration, receiving, however, at each pulfation, only a 

 frriall portion of the whole mafs : the frog, therefore, is 

 now an aerial animal in refpeA to its breathing. 



While thefe changes are going on in the refpiratory 

 organs, feveral others are taking place in different parts of 

 the body. The narrow horny bill, preceded by fmall 

 tlefhy lips, falls off, and its mufcles difappear ; the jaws 

 grow hard, and form a much more ample mouth. 



The eyes, difengaged from that (kin, which only allowed 

 them to appear through a tranfparent diflc, are now feen 

 with their complicated apparatus of three eye-lids. 



The fore-feet, which had been concealed between the 

 bag enclofing the branchis and the peritoneum, appear ex- 

 ternally ; the hind-legs grow every day larger ; and the 

 long tail, formed by fo many mufcular flrata, and fupplied 

 by fuch numerous veffels and nerves, begins to difappear. 

 The inteltines, formerly of nearly uniform fize throughout, 

 exceffively long and arranged in a fpiral mais, become 

 fhort, and are dilated at proper parts to form a ftomach 

 and colon. 



Among thefe changes, which convert the tadpole into a 

 frog, we cannot enumerate the appearance of the generative 

 organs. The tadpole already pofled'es tefticlts, ovaries, 

 and their fatty appendages ; and if tiiefe parts are not fo 

 large as in the frog at the feafon of reproduilion, they 

 approach nearly to their fize at other times of the year. 



What we have jult faid concerning the tadpol§ of tlft 

 frog is equally applicable to that of the toad ; but the dif- 

 ferent fpecies exhibit confiderable varieties in the epocha 

 and the fize at which the change occurs, as well as in the 

 rapidity of the change. The jackie (rana paradoxa) lofes 

 its tail very late, and long after its branchiae ; while the 

 latter do not entirely difappear until it has reached the full 

 fizo of its perfedt llate : the pipa, on the contrary, lofes 

 both very early, and while it is dill very fmall. The fpecies 

 which loie their branchis late, are larger in the tadpole 

 than in the perfcft flate, becaufe thefe fupernumcrary organs 

 fwell out the front of the body, while the tail prolongs it 

 behind. They feem, therefore, to become fma'ler under 

 their inetamorphofis, and grow no more when they huve 

 become frogs. On the other hand, thofe which lofe their 

 tail and branchiae early, have ftill a long time to grow, and 

 may be feen of all fizes in the perfeft ftate. This has given 

 rife to the miftaken notion that the jackie is changed into a 

 fifh ; the tadpoles being larger than the adult frogs, it was 

 not thought poffible that the latter could be the fecond 

 ftate. 



We might rcftore to the larvae of the falamanders the 

 name of cordyli, which they bore among the Greeks, ac- 

 cording to the remark of Schneider. They ought not at 

 leaft to have that of tadpole (tctard), becaufe they have 

 not a large head, their branchiae not being concealed under 

 confiderable coverings, but floating loofely on the exterior 

 of the body. Tiiey are tufts arranged hke the teeth of 

 combs, fimply flefhy or membranous, and attached by 

 pedicles, which allow them to float loofely in the water. 

 The cartilaginous arcs of the fides merely ferve to limit the 

 fmall apertures through which the water pafFes out of the 

 mouth ; for, although the form and arrangement of the 

 tufts feem to expofe them fufficiently to the aftion of water, 

 there are ftill openings from the mouth, enabling the ani- 

 mal to eftablifh a current of the fluid. In other refpefts, 

 the circulation is carried on as in the branchix of the tad- 

 poles of frogs, and it undergoes the fame changes when the 

 branchiae are obliterated. 



The larvae of falamanders, obferved by Cuvier, had the 

 fame vifcera as the adult animals, and pofleffed no horny 

 bill, although their branchiae were ftill very complete. He 

 therefore concludes, that in this refpedl, as well as in their 

 feet, and in the organization and permanence of their tail, 

 there is a much more clofe refemblance between thefe larvx 

 and the adult falamanders, than between tadpoles and 

 frogs. 



Thefe remarks on the .anatomy of the tadpole, and of the 

 larvae of falamanders, are illuftrated by four figures in the 

 I3tb plate of the work quoted above. Figs, i, 2, and 3 

 reprefent the anatomy of the tadpole of the bufo fufcus ; 

 and fig. 4. that of the larva of the falamandra aquatica. 



The co-exiftence in the fame animal of branchiae and 

 lungs, that is, of organs calculated for breathing air, and 

 of thofe which are fitted to extraft air from the water, is 

 not peculiar to the larv^ of frogs and falamanders ; it is 

 obferved alfo in the llren lacertina and the proteus anguinus, 

 two animals whofe conftruftion is in many refpefts fo fingu- 

 lar, that the opinions of naturahfts concerning them have 

 been long extremely unfettled. Many have fuppofed them 

 to be the larvae of feme large reptiles, for which opinion, 



• (Jther 



