REPTILES. 



a contrail docs the lliell or bony cafe of the tortoife form to 

 the fmooth (Idn of the tree-frog ; liow different are the an- 

 nulated (kin of the amplii(bxna, the fcaly covcnnjrof other 

 fcrpents, and the integuments of the toad, rough and tubiT- 



Epidermis. — When we examme what parts ot the body 

 are covered with fl<in in the tortoife and turtle, we can re- 

 cognize it at firft light only on the head, neck, limbs, and 

 tail ; the other parts exhibit to us merely an offeous box or 

 exterior flceleton, incloling the body. But, if we examine 

 more attentively, we (hall find this (keleton covered by an 

 extremely thin epidermis, which may be detached in tranf- 

 parent laminx, fimilar, in figure, to the horny plates, and 

 varying in its coiifdtence in the different (pecies. It re- 

 fembles a fmooth and tranfparent parchm.cnt in the tedndo 

 centrata of Bofc (Daudm, t. ii. p. 153.) The epidermis 

 covering other parts of thefe animals is a fmooth tliin layer, 

 not effentially different from that of the frog and lala- 

 mander, and detached in (lireds feveral times in the year. 



The epidermis of the falamander and frog is a foft thin 

 membrane, covered with a mucous fecretion ; which anfwers 

 a particular ufc in fome kinds, as the rana calamita, enabled 

 by its afhilance to adhere to tlie fmoothed bodies. This fe- 

 cretion, a fimple and innocent mucus, is very different from 

 another, which is found in many reptiles, podeffnig ex- 

 tremely powerful fenfible properties ; the latter is delcribed 

 under the head of peculiar fecrctions, in the latter part of 

 this article. 



The thin tranfparent cuticle of the frog, falamander, and 

 newt, is very frequently changed, being detached in large 

 portions. Blumenbach dates that this change takes phce 

 in the fummer mouths at lead once a week. Specimen, 

 p. 26. 



The epidermis of hzards covers all their fcales, and is de- 

 tached in fmall dried portions, er in larger pieces. It forms 

 alfo a thin continuous dratum in ferpents, enveloping the 

 whole furface, and fpread over every fcale and plate. 

 It is detached annually, at a certain feafon, in a fingle 

 piece, like a (lieath. The call (kin ((lough, exuvise) is 

 turned infide out, fo that its exterior furface is the part 

 previoully in contaft with the true (kin. The animal efcapes 

 at the mouth, which is the only opening by which it can 

 get out of the fheath. The part correfponding to the jaws 

 IS fird detached, and turned back, fo as to expofe to us 

 the fnout, covered by a new (kin. As the head pafies out 

 of its dieath, the latter goes backwards in the fame propor- 

 tion towards the tail, and is thus at lad completely inverted. 

 The tranfparent piece correfponding to the eye (lee an ac- 

 count of the eye) has its concavity outwards. 



Retc Mucofum. — In all reptiles there is, under tlie epi- 

 dermis, a mucous tiflue, of which the colours vary very 

 -much. In the teiludines, for indance, the llvin which 

 covers the feet and neck is not only differently coloured by 

 the rete mucofum, but the fymmetrical fpots, which we re- 

 mark on the fcales, are produced by the fame (ubdance. 

 This we difcover by difiedion. The thicknefs of the (l<in 

 greatly diminifhes as it approaches the bread-plate and the 

 back-ihell. It paffes below the fcales which cover thofe 

 parts, and which are, themfelves, covered by the epidern'.is 

 and rete mucofum ; the variegated colours of which form 

 the fpots which we obferve through the tranfparent parts. 

 A rete mucofum is equally found in the lizards, ferjjents, 

 falamanders, frogs, &c. It is varioudy coloured in each 

 fpecies ; and it prefents often the mod beautiful and charm- 

 ing tints. We find in this clals almoil all the known 

 (hades, even blue, bright red, orange, pearly, gold and 

 filver. 



Reptiles are remarkable for the changes of colour whu... 

 they exhibit, according to the fe-ifon or climate in which 

 they live, or to temporary affedlions of various kinds. In 

 this way the camekon has been mod celebrated, and hai. 

 aftbrded a very trite fubjeft to poet» and moralifls. Tlv 

 changes are, in reahty, very remarkvble, and are particu- 

 larly noticeable when the animal pafles from the (hade into 

 the fun, or vice -verfi, when he is touched, or any thing 

 placed round liim. Sec. 



This property, however, is, by no means confined to the 

 cameleon. Brown long ago obierved it in feveral fpecies of 

 lii^ards (Natural Hidory of Jamaica, p. 462.); and it 

 occurs alfo in reptiles of thele climates. The green iguana, 

 the agame, and . the green lizard, are fomctimes green, 

 fometimes brownilh in their colour. The former is parti- 

 cularly obfervcd in the copulating feafon ; and is loft in the 

 cold and rainy parts of the year. The common tree-frog 

 of Europe exhibits various tints from the brighted emerald 

 green to grey, blueilh, violet, or brown. Other frogs and 

 falamanders change their colours alfo, particularly about- 

 the copulating feafon. 



The Piipilhe. — Reptiles referable birds with refpeft to the 

 papillx ; we find none except under their feet ; they are 

 very thick, and projecting in feveral fpecies of lizards, and 

 particularly in the cameleon. We cannot diftinguifh them 

 m the fea tortoife, which have the feet in the form of fins. 

 They do not exid in ferpents, or at lead have not the form 

 of papillae. 



Cutis. — Reptiles which have the body unfurniihed with 

 fcales, or only partly covered by them, have a very com- 

 paft and denfe (Icin. We have an example in the tortoifes, 

 falamar.ders, frogs, and toads. In the two laft genera, in 

 particular, the cutis is rendered remarkable by not adhering 

 to the body in all its points, as in the other animals, in which 

 it is intimately united with the cellular fubdance. In thofe 

 genera, however, it adheres only at the edges of the mouth, 

 in the middle line of the body, the arm-pits and the groins. 

 In all the other parts the body is free within the cutis, which 

 inclofes it like a fac. 



In lizards and fcrpents we find, as in fifhes, a ftrong cutis 

 under the fcales, even adhering very clofely to the mufcles. 

 Cutaneous Mufcles. — There is no cutaneous mufcle on the 

 trunk of frogs, becaufe the flcin does not adhere to that 

 part of their body. Under the throat, however, we find 

 iome fibres, which are attached to the margin of the jaw, 

 and inferted into the cellular fubdance that unites the (kin 

 to the origin of the bread. 



In tortoifes the cutaneous colli is very vifible, and feems 

 to be formed of two parts ; it is extended from within the 

 concavity of the lower jaw to the bottom of the neck, at the 

 anterior part of the bread-plate. A middle cellular line 

 unites it with the mufcle of the other fide ; it takes its origin 

 from the tranfverfe proceffes of the cervical vertebrje. Benig 

 fpread over all the mufcles of the neck, it ferves as a girdle 

 to them ; in its lower part it is perforated by the demo- 

 madoideus, which, as we have already obferved, arifes from 

 the lateral parts of the bread-plate. 



Secretions of the Skin. — Among reptiles, thofe that have 

 fcales, as fnakes and Hzards, have the (kin almod dry ; but 

 thofe with naked flcins, as falamanders and frogs, have 

 the furface of the body always copioufly lubricated with 

 vifcous matter. 



Toads and falamanders have even the power of augment- 

 ing the fecretion of this liquor, and of making it exude, hke 

 a dew, through the pores of the (Icin. 



The cutaneous glands are more vifible in cold-blooded 

 animals, than in the mammalia. 



The 



