378 



HISTORY OF FROGS, LIZARDS, AND SERPENTS. 



are the most striking peculiarities in the ana- 

 tomy oi a frog ; arid in these it agrees with 

 the toad, the lizard, and the serpent. They 

 are all formed internally pretty much in the 

 same manner, with spongy lungs, a simple 

 heart, and are destitute of the external instru- 

 ments that serve to continue the kind. 



Of all those who have given histories of the 

 frog, Mr Rcesal, of Nuremberg, seems the 

 most accurate and entertaining. His plates of 

 this animal are well known ; his assiduity 

 and skilfulness in observing its manners are 

 still more deserving our esteem. Instead, 

 therefore, of following any other, I will take 

 him for my guide ; and though it be out of 

 my power to amuse the reader with his beau- 

 tiful designs, yet there will be some merit in 

 transcribing his history. 



The common brown frog begins to couple 

 early in the season, and as soon as the ice is 

 thawed from the stagnating waters. In some 

 places the cold protracts their genial appetite 

 till April ; but it generally begins about the 

 middle of March. The male is usually of a 

 grayish brown colour ; the female is more in- 

 clining to yellow speckled with brown. When 

 they couple, the colours of both are nearly 

 alike on the back; but as they change their 

 skins almost every eighth day, the old one fall- 

 ing off in the form of mucus, the male grows 

 yellower, and the female more brown. In 

 the males the arms and legs are much stronger 

 than in the females ; and at the time of coup- 

 ling, they have upon their thumbs a kind of 

 fleshy excrescence, which they fix firmly to 

 the breast of the female. This Linnaeus sup- 

 posed to be the male instrument of generation ; 

 but, by closer inspection, it is found only of 

 service in holding the female in a more strict 

 embrace. It may be cut off, and the impreg- 

 nation continue unimpaired : it is sometimes 

 found in the opposite sex ; and some df the 

 males are found entirely without it ; however, 

 when it is cut off, the male cannot hold the fe- 

 male so strongly as before. 



The sexes couple only once a year : and 

 then continue united sometimes for four days 

 together. At this time they both have their 

 bellies greatly swollen ; that of the female 

 being filled with eggs ; the male having the 

 skin of the whole body distended with a lim- 

 pid water, which is ejected in impregnation. 

 As soon as the male has leaped upon the fe- 

 male, he throws his fore legs round her breast, 

 and closes them so firmly, that it is impossible, 

 with the naked hands, to loose them. The 

 male clasps his fingers between each other, in 

 the same manner as people when they are 

 praying ; the thumbs press with their thickest 

 sides against the breast of the female ; and 

 though she should struggle ever so much, no- 

 thing can induce him to let go his hold. The 



grasp seems involuntary and convulsive ; they 

 cannot be easily torn asunder ; and they swim, 

 creep, and live united, for some days succes- 

 sively, till the female hath shed her spawn, 

 which, at length, she does almost in an in- 

 stant. But how the impregnation is performed, 

 without any apparent instruments of genera- 

 tion, has long been an object of inquiry ; and 

 still continues in great obscurity. To inves- 

 tigate the difficulty as carefully as possible, 

 our German philosopher continued to examine 

 their mutual congress for thre-e years together, 

 and availed himself of all the lights that the 

 knife, or analogy, could furnish. 1 



After having chosen twelve couple of frogs 

 that were thus joined to each other, and having 

 placed each couple in a glass vessel with 

 water, he scarcely let them out of his sight day 

 or night, and even sat up two nights together 

 to examine their operations. The first day he 

 observed nothing that deserved remark : but 



1 Different developments of embryo of Frogs. Dur- 

 ing the cohesion of the two sexes, the female com- 

 mences the deposition of the spawn, which is fecundated 

 during its passage. When first expelled it consists of 

 numerous small opaque globular bodies, enveloped in a 

 small glairy, or glutinous mass. This latter substance 

 soon absorbs a large quantity of water, and, in the course 

 of an hour or two, each becomes not less than a quarter 

 of an inch in diameter. The consequence of this aug- 

 mentation in the bulk of the transparent mass, surround- 

 ing each embryo, is, that all the latter are removed from 

 each other by a whole diameter of each globe ; and they 

 appear like black dots regularly distributed throughout a 

 large mass of transparent jelly. 



The deposit of the eggs takes place at the bottom of 

 the water, notwithstanding the assertion of some natu- 

 ralists, and of Raesel amongst them, that they are expel- 

 led at the surface. The mistake, probably, arose from 

 the mass of eggs being generally found at the surface ; 

 but this arises merely from the disengagement of gas in 

 the substance of the glairy envelope, in consequence of 

 partial decomposition. 



The changes which now begin to take place in the 

 embryo are most interesting. They have been detailed 

 in a very minute and satisfactory manner by Rusconi 

 and I have taken considerable pains during the last 

 spring to follow out his investigations, and by actual ob- 

 servation to correct or confirm his account. I may here 

 observe, once for all, that with the exception of a few of 

 the details in the earliest periods, I have been able to sa- 

 tisfy myself of his correctness; and in those points, I be- 

 lieve that I only failed to do so, partly by my not hav- 

 ing obtained the ova immediately after their expulsion, 

 and partly by the want of time to enter into all the ne- 

 cessary minutiae of the investigation. 



I have also to observe that the development of the 

 young is more or less rapid, according to the tem- 

 perature of the atmosphere ; and that I was enabled to 

 retard or hasten it by regulating this circumstance. I 

 therefore kept my reservoir of eggs in a veiy cold situa- 

 tion, -and occasionally brought a few of them into my 

 drawing-room for the purpose of observation ; in which 

 place, being in an elevated temperature, the development 

 became very rapid. As my object, therefore, was to as- 

 certain positive facts, rather than the periods of the 

 changes, which were dependant upon variable circum- 

 stances, I kept no register of the temperature or of the 

 periods; and I shall, in both these particulars, give some 

 of the statements of the accurate Rusconi. 



