REPTILES. 



difl not altogether prevent it. When three grains of feed 

 were added to twenty-two pounds of water, iome tadpoles 

 were evolved in it, but much fewer than in a ftrongcr 

 mixture. 



As fecundation is effefted in thefe animals by the femuial 

 fluid difcharged in water, it probably is .ilways produced by 

 an extremely fmall proportion. Spallanzani has made fome 

 calculations, in order to find out the cxprifTion in numbers 

 of the quantity of femeii that was efficacious in fame of his 

 experiments. He mixed three grains of fL-minal fluid with 

 eighteen ounces of water, and found that a globule, -s'.jth 

 of a line in diameter, taken out of this mixture, was often 

 fufficient to fecundate a tadpole. The ratio of the tad- 

 pole to the particles of feed difi"uicd in this drop of 

 water, is found to be as 106,4.77,777,7 to one. The weight 



of the feed is ^- of a grain, and its bulk 



199,4.68,750,0 



1 of a cubic line. Diflertations, v. i. j 655. 



300,212,042,0 



He found, however, that .ilthough fo minute a quar.lily 

 of feminal fluid is fufficient to produce the cffecl, there muit 

 be contaft of the grofs and vilible part of the fluid ; that 

 no vapour or effluvium, no aura fpermalka will fuffice. Difl. 

 ch. 5. § 161 — 170. 



The feed of one fpecies will not fecundate another ; that 

 of the water newt has no cffedt on the embryos of frogs and 

 toads ; nor reciprocally : neither is there any aftion of the 

 feeds of frogs on toads, wot njict vsrfd. § 171 — 172. 



The number of eggs is fubjeft to much variety : it is in- 

 confiderable in the ferpents ; from ten to twenty in the 

 vipers and lizards ; one or two hundred in the crocodile, ac- 

 cording to Bartram, Travels in America ; two or three 

 hundred in the turtle ; but the moft numerous in the frog 

 kind. In the toad, where the eggs are laid in a double 

 row, forming a cord of a glutinous nature, thefe rows 

 meafured 43 Paris feet, and contained 1207 eggs. Spallan- 

 zani Difl^. V. ii. § 45. 



In the teft-udines, ferpents, and lizards, which have a 

 true yolk, this is to be regarded as a fupply of nourifhment 

 for the young ammal, whofe evolution probably goes on in 

 a manner analogous to what is obferved in birds ; although 

 the procefs has not been a£lually watched, nor the order and 

 fucceflion of the changes obferved, as in that clafs. Blu- 

 menbach has delineated the egg of the crocodile, with the 

 young one coming forth'; the (hell is flexible, as in the other 

 amphibia, and confiils of a thick, leathery, and tough, ex- 

 ternal fliratum, marked throughout with extremely fine un- 

 dulated lines, and lined by a more delicate fniooth membrane. 

 The recent eggs, and the young crocodiles which they con- 

 tain after evolution has commenced, are eaten by various 

 African tribes. The relation in fize between the egg ( about 

 equal to that of the goofe), and the full grown animal (the 

 Nilotic fpecies), which reaches to thirty feet in length, or 

 even more, is at firil view remarkable ; and Herodotus has 

 called the crocodile the largefl: animal from the fmallelt egg. 

 (Blumenbach's Abbildungen, N°27.) Seba has alfo figured 

 a young crocodile, with the membrane of the yolk adhering 

 to the abdomen, as in birds. Thefaurus, t. 1. pi. IC4, 

 fig. 7. 



In the animals juft enumerated, the eggs, whether depo- 

 fited in the fand of the fea-fliore, or of the banks of rivers, 

 in the holes of trees, the chinks of walls and rocks, &c. 

 undergo no procefs of incubation like thofe of birds, but 

 are developed in the ordinary temperature of the atmofphere, 

 and the young animals come forth from their confinement, 

 differing only in fize and proportions from their parents. 



In the venomous ferpents, and the falamanders, the cafe 

 is different. Tlie egg containing, as in the preceding in- 

 ftanccs, the young animal, and a lufBcient fupply of nutri- 

 n.:ait for its growth, until it is of fize to quit its original 

 abode, is hatched in the oviduft of the mother, and the 

 young come forth from the cloaca alive, but furrounded by 

 their membranous coverings. The young vipers and otiier 

 venomous ferpents, when they are born, are freed by the 

 mother from this kind of after-birth. 



A very curious circumftance has been obferved in fome of 

 thefe, recaUing to our minds the abdominal pouches of the 

 marfupial mammalia, and the mode in which they ferve as a 

 flieltcr for the young, while yet too fmall to ftiift for them- 

 felvcs. Palifot Beauvois thus relates the faft we allude to, 

 " Having perceived a rattlefnake at fome dillance, I ap- 

 proached as gently as poflible, when, on lifting my hand t<» 

 ftrike him, he founded his rattle, opened his mouth, and 

 received into it five fmall ferpents, about the fize of a quill. 

 I retreated and concealed myfelf, when the animal, tliinking 

 the danger at an end, opened his mouth, and let out his 

 progeny. When I appeared again, they immediately took 

 to their fame retreat." He had heard this faft from Ame- 

 rican planters, and it has been fince confirmed by other tra- 

 vellers. Daudin, Hifl:. Nat. des Reptiles, v. 5. p. 68. 



The young of the falamander, like thofe of the viper, are 

 born alive. The female brings forth very delicate oval vefi- 

 cles, which may be compared to hydatids, each of which 

 contains a perfeft young falamander, an inch in length, 

 moving its tail, and lacerating its coverings at the time of 

 birth, and emerging in the form of a tour-footed tadpole. 



" In this fame ftrange animal," fays Blumenbach, " I 

 have obferved a curious fa£l, already noticed by Wurff^bain 

 in his Salamandrologia, p. 83. "viz. that a female, kept by 

 herfelf, and abfolutely without intercourfe with any other of 

 her kind, has produced young ones. I have kept in a glafs 

 at home, for five months, a female falamander, whofe tail I 

 had cut off, and in the mean time have had no other in the 

 houfe, nor even leen one. Yet this folitary female, which, 

 to my furprife, fuftained fo long a fall without growing 

 thin, has begun within a few days to bring forth young, of 

 which thirty-four are now before me, not only living, but 

 very lively. This obfervation will lead us to two conclufions ; 

 I ft, that falamanders really copulate, and that the male doee 

 not fecundate the ova as they are difcharged, like what vre 

 have defcribed in the cafe of the water newts : 2dly, that 

 falamanders have the fame nature in this refpeft as hens ; 

 which, when they have been once impregnated by the cock, 

 will lay fruitful eggs, not for a whole year, as Fabricius ab 

 Aquapendente aflerted, but, according to the moft accurate 

 rcfearches of Reaumur ( art de faire eclorre les oifeaux domef- 

 tiques, t. 2, § S^"]), for five weeks after feparation from 

 the male. 



Thefe young falamanders have a two-edged tail, broadly 

 pinnated on each edge, excellently adapted for fwimming, 

 and funiiflied on each fide of the neck with fimbri- 

 ated branchial appendages like thofe of the tadpole, which 

 however foon diiappear, the two-edged tail being at the 

 fame time converted into a cylindrical pointed one." Spe- 

 cimen, &c. 34. 



All the reptiles of the frog and toad kind, and the aquatic 

 falamanders, have this remarkable peculiarity, to which 

 nothing at all analogous has been obferved in the economy 

 of the warm-blooded clafles or the fifhes : viz. that they 

 undergo a metamorphofis ; and have, in their two ftates, 

 not only an altogether different external form, but alfo 

 important differences in many of the great internal organs. 

 In their firil Hate, they arc little aquatic animals with tails 



afld 



