260 s. GOTO; 



confirmation of those of the latter that I would not have dwelt on tins 

 question so fully, were it not for the fact that mine were made on a 

 species which passes through typical bipinnaria and brachiolnria stages, 

 while the species studied by MacBride passes at most only through a 

 highly modified form of the brachiolaria. We thus see that the 

 behaviour of the pore-canal of asterids is exactly similar to that of the 

 primary calyx pore (Kelchporus) of crinoids [Ludwig '80, Seehger 

 '92, p. 31o] ; and the opinion of Bury ['87, p. 420] that the pore-canal 

 has ''■exis(;ed in a very early stage in the history of Echinoderms, 

 probably before the hydrocœl had arisen," is fully endorsed by what 

 occurs in A. pallida. 



In stage D the condition of the body cavities is essentially the 

 same as in stage C. P)ut the constriction of the left posterior enterocœl 

 from the left anterior has been carried further ; and hand in hand with 

 the rotation of the aboral disc the epigastric enterocœl has also shifted 

 on towards the left side. These tv,'o, tlie aboral disc and the epigastric 

 enterocœl, always go together, the latter lying directly under the former, 

 as may be seen from Fig. 17, PI. XX, which represents some of 

 the frontal serial sections from stage D, ] »laced in order from ventral to 

 dorsal. The partial valve-like septum which we found in stage C be- 

 tween the coalesced left ventral and right horns of the left posterior 

 cavity has completely disappeared, and there is but a single large 

 cavity around the anus (Fig. 17 a & h). We can not, moreover, kn(j\v 

 where to draw the boundar}' line between the right and left posterior 

 enterocœls, and it must be remarked that the [)Osterior cavity next the 

 hydrocœl, marked as the left posterior enterocœl, on the right side of 

 the body in Fig. 17 c may just as well be a portion of the right pos- 

 terior enterocœl, tliough I believe the right liorn of the left postérieur 

 enterocœl has by this time extended so far dorsad as to include this 

 region also. In Fig. 17 d one sees that the anterior and posterior 



