136 THE APODID.E PART 



the coelom epithelium presents no difficuhy, as this 

 epithehuni, on the degeneration of the AnncHdan septa, 

 would naturally form such a continuous membrane 

 through all the segments of the body. The dis- 

 appearance of all the nephridial apertures except the 

 one between the tenth and eleventh segments is a 

 further very natural specialisation. 

 . In summing up the arguments here used in favour 

 of this account of the disappearance of the nephridia 

 in Apus, we have to notice the following points : -- 



(i) The eggs which develop out of the epithelium 

 of the genital glands project, as in the Annelida, into 

 the body cavity and not into the cavity of the genital 

 glands themselves, as one would naturally have ex- 

 pected. This epithelium, then, is a part of the original 

 coelom epithelium of the Annelid. 



(2) The eggs pass again through the epithelium, 

 and travel down the canal formed by it ; this canal has 

 therefore probably taken the place of the nephridial 

 canal which it once covered as coelom epithelium. 



(3) We have to call attention not only to the 

 segmental arrangement of the organs, but to the fact 

 that there is a pair in each segment except in the 

 most rudimentary ; both of these facts agree with 

 what we know of the typical development of nephri- 

 dia in each segment of the Annelida. 



(4) The position of these genital organs be- 

 tween the dorso-ventral muscle dissepiments and the 

 body wall agrees exactly with that of the nephridia 

 of the carnivorous Annelids, which lie in the lateral 

 chambers of the body (see Fig. 11, p. 54). 



