(35) 



this condition exists. 



One thiiit^ is certain; tne fully oevelopea trunk cavity of 

 the Actinot ro c>.a has a distinct inesoaernial linin,, consisting 

 0-^ a somatic and a splaner.nic layer , As far as 1 knov: all 

 Actinotrochae have a ventral raeaentery which, fact tends to- 

 ward tt:e view that the lining, of the cavity of tne trunK has 

 its origin i^ri a sac which grows around the rectum and posterior 

 part of the stomach. Wlr;ether the fact thiat there is an indi- 

 cation of a dorsal meseiitery in the pobterior re;_;ion of some 

 of the fully developed Actiiict rochae, Species, B, , has any bear- 

 ing on the double origin of the cavity of the trunk or not, 

 I cannot say '"or I have never seen the very youn^;^ larvae of 

 this form. 



The youngest larva taken from the tow haa thiree pairs of 

 tentacles with beginnings of tne fourti; pair. In this larva 

 the tentacles naa grown considerably in length and ti.e posterior 

 region had become somewhat elone.ated. (Fig, 31) Only one spec- 

 imen of this age was obtained and I was only able to study it 

 alive. The rresentery between the collar aid lobe v/as plainly 

 seen and there seemed to be a ti:in mesentery between the re.;ion 

 of the collar aad tr.e younger trunk re^^ion. The nephriaial 

 canals were seen with difficulty but the rounded bunches of 

 excretory cells forming tne internal ei.asof zne canals were 



