ASTERIAS PALLIDA. 



26D' 



as may be inferred from a comparison of Fig. IH c & f, between which 

 there are three intervening sections (e;ich = 6-7 /^). The cahbre of the 

 stone-canal is considerably smaller than that of the pore-canal. 



The periœsophageal enterocœl encircles now fully one-half the 

 circumference of the cardiac portion of the stomach. Its dorsal end 

 has grown somewhat over to the right side of the body, and is now 

 enlarged (Fig. l-S e). 



In stages (r to H important changes, the beginnings of which 

 we have seen, are com|)Ieted, and the several organs and cavities attain 

 their definitive positions. The most salient of these changes are the 

 formation of the water-vascular ring, the completion of the stone-canal 

 and of the perioesopliageal enterocoel, and the development of the 

 p)eril)a3mal spaces and of the nervous system. And here at the outset I 

 may state that I regard the two circular perihœmal spaces as of different 

 origin ; I shall tlieref)re call the inner perihœmal ring "circular 

 enterocœl." The justification for this name will be f)und in the 

 following descriptions. 



Hand in hand with the shrinking of the imeoral lobe the an- 

 terior enterocœl becomes less and less spacious, and in Figs. o7-ol),. 

 which arc all taken from a stage intermediate to G and II, it is seen 

 to have become very much flattened in an antero-posterior direction 

 (i.e., oral to aboral). In the interradius of the stone-canal, however, it 

 is still somewluit spacious, and here it persists as the axial sinus, 

 and receives the inner opening ot the pore-canal and external 

 opening of the stone-canal. The anterior enterocud in thus 

 becoming flattened has not been aifected uniforndy in all its parts^ 

 but its right and posteri(jr portion lags behind the rest, as can 

 be seen from Figs. o7, 08, and o!), the latter of which is pretty nearly 

 the frontal section. When the flattening of the anterior enterocœl has 



