GENERATION OF ANIMALS, III. i. 



servation that neither in birds nor in fishes do the 

 fetations attain perfection for the purpose of genera- 

 tion apart from the males ; with regard to fetations 

 being formed apart from the males in fishes as well, 

 this has been observed, though to a less extent, to 

 occur, but it has been noticed most in the fresh- 

 water fishes." Some of them, as we can see, have 

 eggs from the very outset, as is recorded in the 

 Researches.^ Speaking generally, in birds at any 

 rate even the impregnated eggs usually do not grow 

 unless the hen is trodden continually. The reason 

 for this is, that, just as in the case of women inter- 

 course with the males draws down the discharge of 

 the menstrual flow (since when the uterus has been 

 heated it draws '' the Uquid and the mouths of the 

 passages are opened), so with birds : the same thing 

 occurs ; the menstrual residue advances little by 

 little. It is not discharged externally because there 

 is not much of it and the uterus is high up towards 

 the diaphragm, but it runs down and collects in the 

 uterus itself. This liquid, of course, which percolates 

 through the uterus, makes the ^gg grow, just as that 

 which passes through the umbilical cord makes the 

 embryos of Vi\ipara grow, for when once the birds 

 have been trodden, they all continue almost always 

 to have eggs, albeit quite small ones. In \iew of this, 

 some people are in the habit of saying that wind- 

 eggs are not formed (independently) either, but are 

 merely reUcs of an earUer impregnation. This how- 

 ever is untrue. It has been sufficiently established by 



" The reference to the erythrinits which several mss. have 

 at this point is out of place ; cf. H.A. 567 a -21. 

 * At H.A. 567 a 30. 

 ' See above, 739 a 35 fif., esp, b 1 1 ff. 



275 



