146 THE APODID^E PART i 



groups again (e.g. the Cirripedia) have returned to, 

 or retained, the thread-shaped spermatozoa of the 

 Annelida. 



In the development of the eggs and of the sperm 

 here described, we find but little positive evidence of 

 the relationship which we seek to establish. But we 

 must again repeat that it is enough for our argument 

 if nothing actually contradicts it. It rests upon an 

 accumulation of homologies which are hardly to be de- 

 nied, some of which, indeed, have long been recognised 

 though never before carried out in detail. It is enough 

 if we show how the other parts of the organisation 

 of Apus can be deduced from organs of an Annelid. 



With regard to the origin of the sexual products, we 

 have shown more than this. We have drawn attention 

 to at least one point in which Apus agrees with the 

 Annelid, and that is, in the development of the egg, not 

 into the genital tube, which did not exist in the 

 Annelid, but into the body cavity. The point may 

 seem to be a small one, but every one who has worked 

 out the anatomy of Apus will, we are sure, have been at 

 once struck by the fact, that although the genital glands 

 are large and extensible, yet the eggs bud outwards 

 and not inwards. It was this striking method of 

 development of the eggs which first led us to homo- 

 logise the epithelium of the genital tubes with the 

 ccelom epithelium of the Annelida. 



The egg, as already described, consists of one egg- 

 cell and three nutritive cells. As the nutritive cells are 

 probably modified egg-cells, the eggs of the original 

 Crustacean-Annelid may have developed out of its 



