REPTILES. 



and large heads ; from tlieir tvvidiug movements of the 

 former, and the great fi/.e of the latter, tliey have been 

 called III Latin gyrini, in French tctards : the Englifli name 

 is tadpoles, and tlie German kaul([ua[>iK'n. 



Dev.'lopcinent of th^ Fro^. — As the Ipawn of frogo is de- 

 pofited in ponds, ditches, or other llagnant water, the con- 

 tamed ova are evolved in the ordinary temperature of the 

 atmofphere. In one fpecies of toad, Spallanzani fays, that 

 it proceeds at 6° above freezing of Reanmur. He found 

 that a temperature of iii^ Fahrenheit, did not interfere 

 with the iubfequent evolution ; tliat the number of tad- 

 poles produced was much diminilhed ;\fter expofure to 122"; 

 and that very few were erolved after the eggs had been 

 immerfed in water of 132°. A heat of in" was fatal 

 to tadpoles and frogs; although the latter bear 111-' in 

 the warm fprings of Piia. (Trafts, vol. i. p. 32.) Each 

 egg lies in the centre of a tranfparcnt fpherical mafs of 

 mucilage ; many of which, aggregated together, form what 

 is called frog's fpavvn. Round the eggs are two concentri- 

 CJ^l membranes, of which the innermoll, when pierced with a 

 needle, difcharges a fluid as limpid as water. The egg is 

 round, and has a fmootli furface, of which one hcmifphere is 

 black, and the other white. When the hot feafon is far 

 advanced, the obferver foon perceives the lineaments of the 

 tadpole. The egg grows for fome hours without lofmg its 

 round fliape : it is next elongated ; the white hemifphere 

 becomes darker, and the black changes into a longitudinal 

 furrow, terminated by two perpendicular procefles. And, 

 as it increafes in bulk as well as length, the internal circular 

 membrane is dilated, and contain'; more fluid. By tracing 

 thus the progrefs of the evolution, we come to perceive 

 that thefe bodies are not eggs, as naturalifts fuppofe, but real 

 tadpoles. The furrow and the procefles become longer ; the 

 fuppofed egg affumes a pointed figure, the whitilh hemifphere 

 dilates, and the black is incurvated. The pointed part appears 

 to be the tail of the tadpole, and the other the body. Further, 

 the oppohte end takes on the appearance of the head, in 

 the fore part of which the form of the eyes is vifible, 

 though they are yet clofed. The two procefles alfo, by 

 which the animal faftens itfelf to bodies, when it is tired 

 of fwimming, become evident, as likewife the vellige of 

 the aperture of the mouth, and the rudiments- of the gills. 

 As the organs are further unfolded, the tadpole, which 

 has not moved hitherto, begins to ftir, and loofen its fetters ; 

 at this time it appeai:s clearly, that the internal circular 

 membrane is the amnios, in the liquor of which the tadpole 

 floats ; the umbiHcal chord at laft is feen, and becomes ftill 

 more vifible the firit day after the animal has quitted his 

 confinement.' The cord is not, as in other animals, at- 

 tached to the belly, but to the region of the head. (Spal- 

 , lanzani's Difl'ertations, v. 2. ^ 14 — 16.) We take the 

 liberty to note what is here faid about the umbilical cord 

 as a fubjeft for further refearch. 



The branchix are vifible towards the end of the fixth day ; 

 in the courfe of the feventh and eighth all the tadpoles quit 

 „, the vifcid fubftance, which had been floating on the water, 

 Ik and which had hitherto ferved them for food. By the 

 H, fourteenth and fifteenth days they are fo much grown, that 

 B. two fmall but prominent eyes, an open mouth, noltrils, &c. 

 H can be diftinguifhed. About the nineteenth and twentieth 

 H days the branchial appendages are withdrawn within the 

 flcin, and no longer vifible. The heart can be feen to move, 

 and the caudal vertebrae are recognifable. On the twenty- 

 fourth day the front limbs, which had already exifl;ed under 

 the integuments, appear in the place of the branchise, or 

 rather near where they had been. In ten or twelve days 

 more the hind limbs come out. In this ftate they fwim 

 Vol. XXIX. 



about in the water, and grow. The tail gradually dil- 

 ap[iear5, and in about two months after they have been 

 hatched, they are metamorphofed into frogs. Thefe at 

 firll are fmall, and tlicn become gradually larger. Except 

 in the cafe of the raiia paradoxa, and the bufo fufcus, in 

 which the tadpoles become fo large, that the animal, when 

 it lias changed, is of the adult fize. 



Anatomy of the 'iadpole. — The points in which the animal 

 diflLTS from the organic arrangements of its perfeft flate, 

 are the large tail, which bears a very confidcrable proportion 

 to the body, and is afterwards entirely loft ; comparative 

 imallnefs of the mouth, to the under lip of which a fmall 

 organ I1 attached for fixing the tadpole to other objeAs ; 

 a kind of horny plate tor jaws ; two tuberofities under the 

 neck, which the animal can diltcnd at pleafure ; the rudi- 

 ments of the lungs ; the intellines convoluted in a fpiral 

 mafs, which iwcUs the abdomen, and far exceeds, in its 

 ratio to the length of the body, the inteilinal canal of the 

 perfedl animal ; the branchial appendages, and the veflels 

 connefted with them ; the fore hmbs, fituated at nrft under 

 the flcin. For the feries of changes, and the anatomy of 

 the young animal, ice the plates of Roefel, Hift. Ranar. 

 Noftrat. 



Further part'u ulars of the anatomy of tadpoles, and par- 

 ticularly of the circulating and refpiratory organs. In his 

 " Recherches fur les Reptiles douteux," Ouvier has entered 

 at fome length into a confideration of the anatomy of the 

 tadpole. The following account, which is tranflated from 

 his memoir, as pubhlhed in the " Recueil d'Obfervations de 

 Zoologic et d'Anatomie comparee, faites dans le Voyage 

 de Humboldt et Bonpand," v. i. p. 195, is to be under- 

 fl:ood as applying to the full grown tadpole. 



The tadpoles of frogs, tree-frogs, and toads, differ 

 from thofe of falamanders, principally in having their 

 branchii concealed : we have already obferved, that in their 

 earlier fl;ages the branchiae of the former are alfo external: 

 the only vi'ay by which the water can efcape from them 

 is through two holes, formed in diff^erent fituations, accord- 

 ing to the fpecies : there are even feveral which have only 

 one hole, on the left fide. Such are the tadpoles of the jackie 

 (rana paradoxa), and of the brown toad (buco fufcus) ; 

 but the tadpole of the common frog has two, both placed 

 below. 



We find, on opening the fl:in of a tadpole longitudinally, 

 that the internal organs are divided into two parts, or con- 

 tained in two membranous facs. 



The firft extends from the horny and falfe jaws, which 

 form the mouth of the tadpole, to behind the branchia:> 

 enveloping the latter entirely. The other contains the 

 abdominal vifcera ; it is the peritoneum, on which veftiges 

 of the abdominal mufcles are already vifible. 



The firft; fac is very thin and tranfparent, and penetrated, 

 like the flcin, by holes for the exit of the water from the 

 branchiae. 



The latter form on each fide four tranlverfe rove's of 

 fmall tufts or fringes, fupported by the fame number of 

 fmall cartilaginous arches, which are marked on the fide 

 next to the mouth by fmall rounded tubercles. Thefe 

 cartilaginous arcs are articulated on one fide behind the 

 cranium, on the other to a fpecies of os hyoides, and have 

 the fame motions as in fifties. In their intervals the water 

 can pafs freely from the mouth to the branchii, to be 

 difcharged fubfequently through the fmall external apertures. 

 The organization of the branchise in the tadpoles of 

 frogs is, therefore, the fame as in certain fifties, for example 

 the callionymi and others, where the water can only pafs 

 out by narrow apertures ; there is, however, this difference, 

 SC that 



