272 Herr F. Leydig on the Brood- cavities 



From tlie above-quoted observations upon " Pipa americana 

 and Pipa africana " Mayer derives the conception that for 

 the process of the incubation of the eggs in the first place the 

 dorsal epidermis peels off, and that afterwards, when the ova 

 are lying in the cells, a new and thicker epidermis appears to 

 be produced, which then gives rise to the opercula of the cells. 

 We should probably not be mistaken in assuming that the 

 structures which the author terms " pits and little cavities in 

 the skin " are related to the cutaneous glands ; and from this 

 we may conclude that he was inclined to regard the larger 

 cutaneous glands as the origin of the subsequent brood- 

 cavities. Yet we are left in doubt upon the point. It is also 

 worthy of note that he derives the opercula of the cavities in 

 two different ways : in the first communication he compares 

 them to the " cornea," according to which they should be 

 composed essentially of connective tissue ; while in the second, 

 on the other hand, he declares that they are a part of the 

 epidermis, and consequently they should be of an epithelial 

 nature. 



A few decades later Wyman published a memoir on the 

 development of Pipa americana, which is not accessible to 

 me ; I regret this the more, since the author in question is 

 said to have dealt exhaustively with the subject *. However, 

 it is stated that the result of his investigation tends to show 

 that the formation of the alveoli is traceable " to a process 

 of invagination of the skin." 



Much about the same time investigations upon the dorsal 

 integument of Pipa were likewise instituted by myself ; and 

 as I came to a different conclusion, I venture here to reproduce 

 verbatim the statement I then published f : — 



" The hone^'comb-like cavities upon the back of Pipa dorsi- 

 gera, in which the development of the young takes place, must 

 be regarded as enormously developed cutaneous glands. I 

 examined a female whose eggs were still in the ovary and 

 another with the embryos already far advanced within the 

 dorsal alveoli. In the former specimen one observed in the 

 dorsal integument the same spherical glands, with narrow 

 efferent ducts through the epidermis, as were seen in the skin 

 upon the rest of the body. As compared with what we find 

 in the case of other Batrachians, the glands are by no means 

 closely packed, but, on the contrary, are somewhat widely 

 separated. Between the glands the skin is elevated into 

 papillae of varying size. In the case of the second animal 

 the glands in question were no longer present upon the back, 



* Vide ' Silliman's Journal,' ]8o4. 



t Leydig, ' Lehrbuch der Histologie/ 1857, p. 80, 



