of an Asterid with Large Yolkij Ejjs. 389 



In tliick sections the yolk is not nearly so apt to be broken, 

 nor is there such a liability in fuldiiig, but there is a greater 

 liability to curl. The sections were then mounted on the slide 

 in hot water to flatten them. They were stained in hsema- 

 tosylin, then washed in running tap-water till tlie excess of 

 stain was removed and until they took on a deep blue colour. 

 They were then doubly stained in eosin (watery solution) . 



By such procedure very successful results in staining 

 were attained and the differentiation between yolk and 

 tissue shown up clearly and distinctly. 



Internal Ajiatomij. — The type of development conforms 

 exactly to that shown in Asterina gibbosa as described 

 by MacBride *. The chief difference is that the embryos 

 under discussion are much larger in size and have all the 

 interstices of the body gorged with yolk. The coelomic 

 cavities^ hydrocceles (both right and left), perihccmal spaces, 

 the stone-canal, and pore-canal all have developed in a 

 similar manner to that which has been described in the 

 case of Asterina. PL XII. fig. F shows the relaiions of the 

 coelomic spaces. The right posterior coelom {r.p.c.) is placed 

 dorsally; the left posterior coelom {l.p.c.) with its right ventral 

 horn {l.'p.'c.') extends over to the right on the ventral surface. 

 Between these two portions of the left coelom is seen the 

 remains of the old anterior coelom, now the axial sinus iax.), 

 with the stone-canal {st.c.) on its posteriorwall. The develop- 

 ment of all these structures is the same as in the case of 

 Asterina and by their further growth and changes leads to 

 similar alterations in the structure of the orgaTiism. 



The periheemal spaces are deiived froui evaginations of the 

 coelom, four arising from the left posterior and one from the 

 anterior coelom. PI. XII. fig. F shows one [ph. 1-5) deve- 

 loped from the left coelom and also one {ph. \-.i) developed 

 from the anterior coelom [ax.). These tongue-like projections 

 of coelom insinuate themselves between the lobes of the 

 hydrocoele and the ectoderm from either side and finally 

 meeting beneath the floor of the hydrocoele form a septum. 

 PI. XIII. fig. G serves to illustrate another point, viz. the 

 relation of the preoral cavity to the axial sinus. The con- 

 striction of the preoral lobe or stalk from the body is effected 

 by opposite sides of the stalk becoming approximated to each 

 other and folded, so that portions are invagiuated into the 

 interior and destroyed by histolysis. This process causes 

 the anterior coelom to become divided into two portions — 



* E. AV. MacBride, "The Devekipmeiit of Asteriim ijlbbom;' Q. J. M. S. 

 18DG. 



