GENERATION OF ANIMALS, 11. vn. 



mistaken. If this were true, the same would occur 

 in the other animals, but it is not found to do so, as 

 can be easily observed by means of dissections. Also, 

 all embryos alike, whether they be of animals that 

 fly or swim or walk, have round them fine membranes 

 which separate them from the uterus and from the 

 fluids which are formed there ; and there is nothing 

 of the sort in these membranes nor can the embryos 

 get the benefit of anything whatever through them. 

 As for embryos that are produced by means of eggs, 

 it is of course obvious that in all cases their growth 

 takes place outside the uterus, after they have been 

 separated from it. 



The partners in copulation are naturally and ordi- Hybrids, 

 narily animals of the same kind ; but beside that, ®*'^' 

 animals that are closely allied in their nature, and are 

 ryot very different in species, copulate, if they are 

 comparable in size and if their periods of gestation 

 are equal in length. Although such crossing is in- 

 frequent among the majority of animals, it occurs 

 among dogs, foxes, wolves (and jackal';) : the Indian 

 dog " also is produced from the union of a dog ^^^th 

 some \\i\6. doghke beast. It has also been observed 

 to occur among those birds that are salacious, e.g., 

 partridges and common fowls. A case among the 

 crook-taloned birds is that of the hawks, different 

 species of which copulate, as it appears ; and the 

 same occurs among certain other birds. We have 

 no trustworthy observation of its occurrence among 

 sea-animals ; but there is a strong suspicion that 

 the rhinobates as it is called is produced by the copu- 



be no general agreement as to what this animal was ; see 

 Piatt's note, C.Q. Ill (1909), 241 S. Cf. too the " Laconian 

 hound," 738 b 31. 



243 



