ASTERIAS PALLIDA. -"^ 



enterocœls of the left side are separated only by a valve-like partial 

 septum, and the complete separation of these two cavities is effected by 

 the oTowth of this septum. In Fig. 17 ß we see that the separation of 

 the epigastric from the riglit posterior enterocœl is not yet .quite 

 thorough, the two being still connected by a two-layered cellular 

 membrane like the sero-amniotic connection of vertebrates. There 

 has also been a change in tlie outline form of the coalesced left and 

 right posterior enterocœl as seen from the left side. In this stage (D) 

 namely, the margin of the aboral disc presents five rcKinded pro- 

 tuberances which are to become the arms of the star ; and into each of 

 these protuberances the coalesced left and right posterior cavity sends 

 out a, diverticulum (Fig. !)). 



The epigastric enterocœl has gr«nvn somewhat more and has 

 become more nearly circular, than in stage C, but it is still very 

 flattened and is confined more to the dorsal side of the body, so that 

 it does not appear in para-frontal sections passing through the most 

 ventral portion of the body (Fig. 17 a & J>). 



Henceforth, i.e., after the complete isolation of the epigastric 

 enterocd'l, I shall call the coalesced cavity consisting of the whole left 

 posterior enterocœl and the part of the right posterior enterocœl that 

 remains afler the isolation, the " secondary left posterior enterocœl." 

 TMiis is in stage D still in open conununication with the anterior 



enterocœl. 



The periœsophageal enterocœl is nearly in the same tulmlar con- 

 dition that it was in stage C. It is, however, now entirely or almost 

 entirely cut off from the left posterior enterocœl, being in the latter 

 case connected with it by a solid string of cells. It has also grown 

 more towards the ventral side, so that it now encircles inore than one- 

 half the circumference of the cardiac portion of the stomach. 



The stone-can;d has been constantly growing away from the inner 



