the Development of Anableps GronoviL 441 



and grows until it acquires the length of an inch and a 

 quarter, which gives the size of the longest foetus which 

 our specimens furnished. Even the umbilical sac and the 

 fissure which succeeds it, continue to grow after the yelk 

 has disappeared. As a general rule among oviparous fishes, 

 the yelk supplies all the material required for the growth 

 of the foetus ; and the same holds good with regard to 

 nearly all Batrachians,* to scaly Reptiles and Birds. So 

 general has this rule been believed to be, that none but Mam- 

 mals have been supposed to contribute any thing beyond 

 the materials of the egg to the support of the young. But 

 recent observations go to prove that some fishes, such as 

 the Torpedo among the Plagiostomes, the Embiotoca 

 among osseous fishes, are to be placed in the same category 

 as Mammals, in relation to the fact of being nourished by 

 the parent during gestation, although neither a placenta is 

 formed nor does any direct vascular communication what- 

 ever exist between the foetus and the maternal circulation. 

 We cannot explain the growth of the foetal Anableps by 

 any other hypothesis than that it is nourished by a fluid 

 secreted by the walls of the sac in which it is lodged in the 

 earlier stages, or by the parietes of the general ovarian cavity 

 in which the foetuses are received towards the end of ges- 

 tation. The high degree of vascularity of the egg-sac is 

 favorable to this supposition. As the body of the foetus, at 

 a very early period, becomes covered with scales, absorption 

 could only take place through the intestinal canal or by the 

 surface of the yelk-sac, which invests the viscera and 

 increases in size for a long period after the yelk itself has 

 wholly disappeared. In the later stages of gestation, even 

 the yelk-sac is out of the question, since it in turn wholly 

 disappears, while the foetus occupies the general cavity of 

 the ovary. 



* The only exception among Batrachians, as yet noticed, is found in the 

 Pipse of South America. See Observations on Pipa Americana, by Jeffries 

 Wyman, M. D., in American Journal of Science, 2d Series, vol. xvii. p. 369. 



JOURNAL B. S. N. H. 57 



