436 R. M. PACE. 



been studied by Hincks (13), Redfern (22), Jobet (14), 

 Barrois (2), and Prouho (20), but the first four authors 

 studied only the living larva, of which Barrois has given an 

 excellent account with numerous figures, while Prouho, who 

 has described the later stages of the larval history in detail, 

 has paid but little attention to its earlier stages. 



The research was undertaken at the suggestion of Dr. S. F. 

 Harmer, with the view to determine whether that structure 

 overlying the internal sac in the mature larva of Flustrella 

 is to be regarded as a stomach comparable to that which he 

 had described (11) as present in Alcyonidium. As the 

 work proceeded it has seemed expedient somewhat to extend 

 its scope, and to follow out the history of the egg from its 

 first appearance ; and the presence of a " yolk-nucleus " being 

 detected, this structure has also been studied in some detail. 



The work, which has been conducted partly at Cambridge, 

 partly at Plymouth, and partly at Brighton, has been greatly 

 assisted by a grant from the Government Grant Committee of 

 the Royal Society, to whom my best thanks are due. I would 

 also take this opportunity to express my thanks to Dr. 

 Hai'mer for his kindly interest and criticism, and for the loan 

 of some of his own preparations of later larval stages, aud for 

 permission to reproduce one of his drawings (PI. 25, fig. 65 a), 

 to Dr. E. J. Allen for granting me the use of a table at the 

 Plymouth Laboratory of the Marine Biological Association, to 

 the authorities of Newnham College, Cambridge, for per- 

 mission to work at the Balfour Laboratory, and to Prof. J. 

 Graham Kerr, Dr. E. G. Gardiner, and Mr. W. Wallace, for 

 advice on technical points. 



Material and Methods. 



Collecting Material. — The material on which this paper 

 is based was collected at the following places and dates : 

 Swanage, March, 1902 ; Totland Bay, Isle of Wight, April, 

 1903; Plymouth, February to April, 1903, February to July, 

 1904; Brighton, May to July, 1903. 



