398 PR ARTHUR T. MASTERMAN ON THE 



Central ccelom. — We now come to the question of the small sac-like portion of the 

 ccelom which is constricted off from the posterior wall of the anterior ccelom in stage B, 

 here termed the central ccelom. This is evidently the ' dorsal sac' of Bury, # the 'schizoccele 

 vesicle ' of FiELD,t and the ' right hydroccele ' of MacBride.;}; It agrees closely in origin 

 and appearance with the last of these. MacBride finds that the right hydroccele arises 

 in Aster ina on the dorsal border of the right cceloraic wing, a position taken up by the 

 central ccelom in Cribrella soon after its first appearance. Apart from its origin, it is 

 evident that if the epigastric ccelom is to be regarded as the homologue of the hydro- 

 ccele, it is impossible for the central ccelom to also occupy this relationship. As regards 

 its origin, if we may suppose that it is a little later and more modified in development 

 in Asterina, then MacBride's facts of development would fall into line with mine. 

 Goto § finds the dorsal sac arising as a diverticulum from the left posterior ccelom, 

 or rather from the junction of left anterior and posterior cceloms. This is very nearly 

 the position in which I find it, and I think that a median organ such as this could quite 

 easily be dragged over to the left by. the more rapid growth of the left ccelom (hydro- 

 ccele), just as in stage C of 'Cribrella the anterior opening of the mesenteron is dragged 

 over to the left. MacBride's evidence for a right hydroccele obtained from abnormal 

 larvae is weakened by the fact that it is impossible to tell from what part of the ccelom 

 the abnormal right hydroccele is developed : it does not appear impossible from some 

 of his figures that the right anterior ccelom gives off the right hydroccele comparable 

 to the epigastric ccelom. 



In any case I think the facts, either according to MacBride or Goto, are not opposed 

 to regarding the central ccelom as a primarily median organ. 



Pre-oral coslom. — The structure of the remainder of the anterior ccelom, and its 

 conversion into pre-oral ccelom, axial sinus, pore-canal and stone-canal agree so closely 

 with the researches of Bury, MacBride and Goto that further remark is unnecessary 

 except to further point out that the development of the perihsemal ccelom 4/5 from the 

 axial sinus agrees also with MacBride, confirmed by Goto. 



We may sum up the origin and fate of the ccelomic elements in Cribrella as 



follows : — 



Larva (Stage D). Starfish (Stage F). 



Anterior ccelom/ Ei S ht lateral ccelom = Epigastric ccelom. 



x v \Pre-oral ccelom = Part lost ; remainder gives axial sinus, pore-canal, 



stone-canal and perihsemal 4/5. 

 Central ccelom = Pericardium. 



Left lateral ccelom = Hydroccele. 



t, ■ ' . , /Right posterior ccelomX-tj , . , 



Posterior ccelom^ ° r >Hypogastric ccelom. 



\Left - •„ „ / 



\Oral ccelom and four penhsemals. 



*'Bury,'H., "Sudies in the Embryology: of Echmoderms," Quart.- Jour n. Micr. Sci., April 1889. 



t Field, G. W., " The Larva of Asterias vulgaris" Quart. Journ. Micr. Sci., vol. xxxiv., 1894. 



X MacBride, E. W., "The Development of Asterina gibbosa," Quart. Journ. Micr. Sci., xxxviii., 1895-6. 



§ Goto, S., Journal of the College of Science, Imp. Univ. Tokyo, Japan, vol. x. part iii., 1898. 





