ON THE DEVELOPMEXT OF SOME STARFISHES. 553 



PAPERS, 



27. Notes on the Development of the Starfishes Asterias 

 cflacialis O. F. M. ; Crihrella oculata (Linck) Forbes ; 

 Solaster endeca (Reti^ius) Forbes ; Stichaster rosevs 

 (0. F. M.) Sars, By James F. Oemmill, M.A., M.D., 

 D.Sc, F.Z,S.* 



[Received M«,y ^0, 1916:: Read Novemlx!.!- 7, 1916.] 



(Plates L & Il.t) 



Index. r. 



irage 



Asterias glacialis 553 



Cribrella oculata 654 



Solaster endeca 560 



Stichaster roseus .gg3 



I. Asterias glacialis. (PI. I.) 



In the course of attempts to rear Asterias glacialis I have 

 constantly noticed that in the early larvaB (6-8 daj'-s) a small mass 

 of cells takes origin from the wall of the stomach dorsally on the 

 left side. Although this mass usually disajopears by breaking np 

 into mesenchyme before the main coelomic cavity has extended 

 back into its neighbourhood, still not infreqnently some of its 

 cells can be seen to join the wall of the ccelom. It is very 

 cornmon for the mass in question to show traces of a central 

 cavity after its separation from the stomach and before its 

 disruption into mesenchyme. 



A similar mass, but rather smaller and less constant, occurs in 

 the case of Asterias ruhens (2, p. 233), and two such masses, right 

 and left, are frequent in the larva3 of Pomnia (3, p. 32), In'all 

 three species considerable variation in the constancy and size of 

 the masses is exhibited by difierent broods of larva? as well as by 

 diiferent larva? in the same broods. 



The object of the present note is to call attention to an 

 instance in which the mass was unusually well-marked in prac- 

 tically all the early larvje belonging to a particular culture of 

 Asterias glacialis. Later, in a large proportion of the larva?, the 

 mass as it separated off from the st-omach acquired a distinct 

 lumen, and, subsequently increasing in size, fused with the 

 coelomic cavity of the left side, thus taking a share in the actual 

 formation of the posterior portion of the cavity in question. 

 Stages in the process are illustrated in PI. I. figs. 1-5, and 

 explained in the description attached. 



* I have to express indebtedness to the Trustees of the Carnegie Trust for "rants 

 towards the expen.ses incurred in this investigation, as well as in that on '^" The 

 dilation of Asterids and the Question of Ciliary Nutrition in certain Species" (Proc 

 Zool. Soc. Lond. 1915). 



t For explanation of the Plates see p. 564, 



Proc. Zool. Soc— 1916, No. XXXIX. 39 



