GENERATION OF ANIMALS, III. xi. 



the female parent " or from part of the fetation ^ ; 

 so that if the former way is impossible (i.e., if it 

 cannot flow to them out of the earth as it flows to 

 animals from the mother), of necessity they must get 

 it from part of the fetation, and generation of this 

 sort we call generation from an egg. Thus much, 

 therefore, is plain : if there were a " principle " of 

 their generation in the case of all animals, we should 

 reasonably expect it to be one or other of these two, 

 larva or egg. It is, however, less reasonable to hold 

 that their generation would take place out of eggs, 

 because in the case of no animal do we observe this 

 sort of generation '^ to occur, whereas we do see the 

 other, in the case both of the blooded animals I 

 mentioned •* and the bloodless ones. Under this 

 latter heading come certain of the Insects, and also 

 the Testacea with which our discussion is concerned : 

 they are not formed out of a part of something as 

 are the creatures produced from eggs, and further, 

 they effect their growth in a similar way to larvae, 

 for larvae grow towards the upper part, towards the 

 " principle," the nourishment for the upper parts 

 being in the lower part. In this respect they re- 

 semble the creatures that are produced from eggs, 

 except that the latter use up the n-hole of the egg, 

 whereas, in the case of those produced from larvae, 

 when the upper part has grown by drawing on the 

 substance in the lower part, then the lower part 

 becomes articulated out of what remains. The 

 reason for this is that (not only in the early stages 

 but) afterwards as well * the nourishment is produced 

 in the part below the diaphragm in all animals. 

 That the larva-like creatures effect their growth in 



*' Cestreus and eels. ' When they are fully grown. 



363 



