GENERATION OF ANIMALS, III. in.-i\-. 



the creature was still enveloped in the egg, the 

 passages extended to the uterus. This occurs, as we 

 have said, in the smooth dogfish.* 



I have now mentioned the respects in which the 

 process of generation of fishes differs from that of 

 birds, and also the causes thereof. Otherwise, they 

 both follow the same course. The fishes have one 

 of the two umbiUcal cords, just as the birds have (in 

 birds it connects with the volk, in fishes with the 

 entire egg, because the fish's egg is all single-coloured 

 and lacks the distinction into white and yolk), and 

 they obtain their nourishment by means of this ; as 

 it gets consumed the flesh in like manner encroaches 

 upon it and grows round it. 



I have now described the manner of formation of 

 those fishes which produce a perfect egg internally 

 and are \aviparous externally. 



The majority of the remaining fishes are externally IV 

 oviparous ; and all of them except the fishing-frog jf\^^^''* 

 produce an imperfect egg. The reason for this excep- 

 tion I have given earlier.'' I have also given the 

 reason whj- the others produce imperfect eggs.*^ 



So far as the process of formation is concerned, the 

 development from the egg follows the same lines as 

 the internally oviparous Selachia, except that they 

 start very small and grow very quickly, and the out- 

 side of the egg is harder. The growth of the egg is 

 like (that of) larvae, for those animals which produce 

 larvae produce something small to start with, which 



Muller in the 19th century (see J. Miiller, i7ber den glatten 

 Hai des Aristoteles, Berlin, 1843 ; paper read Apr. 1839 

 and Aug. 1840). An account of the discovery, with Miiller's 

 letters, is given by W. Haberling, Archiv f. Gesch. der Math., 

 der Naturw. iind der Technlk, 10 (1937), 166-184. 

 » At 754 a 26. " At 718 b 8. 



303 



