nor rudiment of such, the ectoderm under their tips 

 being as yet undifferentiated from the oral disk. 



The hypoga .trie enteroccele has assumed a more 

 pentagonal shape than in "D" , it having grown out 

 over the radial water canals. These projections )f 

 the hypogastric enteroccele till continue to grow 

 with the growth of the arr.s and become the brachial 

 extensions of the body coelome. 



The interradial pouches of the hypogastric en- 

 terocosle , which were beginiag to form in "D" ,have 

 pushed down further and further between the radial 

 canals until, coming in contact with the ventral 

 ectoderm, they bend over inserting themselves be- 

 tween the ring canal and the oral disk .Figs. 17-21. 

 hip ,1-2,2-3,3-4 and 4-5. In the same way the pouch 

 frn- tv jmr'n from the anterior enterccoele has 

 grown under the water rins in the stone canal inter- 

 radius. In theesc .f ive interradial onterocoelic eut- 

 growths,as has been mentioned before, we have the 

 rudiments of the outer psrihaemal sinus of the adult. 

 The process by which this perihaemal sinus is form- 

 ed in Ophiura brevispina agrees in every detail with 

 its method of origin in Asterina sibbosa as describ- 



