598 E. W. MAOBUIDE. 



ciliated band, chiefly of the left half thereof, Avhich grows 

 pari passu Avith the left hydrocoole. The outer part of the 

 larval oesophagus opeus out in consequence of the shrinkage 

 of the forehead to form an atrium into which the primary 

 hydrocoele lobes project. 



(11) The larval intestine slowly diminishes in size and 

 degenerates, this process being accompanied by a vacuo- 

 lisation of its cells. The larval stomach becomes pushed 

 over to the right — a process which leads to the same result 

 as the moving of the larval mouth to the left in Holothu- 

 roidea, or the formation of the adult mouth on the left 

 in Asteroidea and Echinoidea. 



(12) The primitive germ-cells originate from the left 

 posterior coelom covering the stone-canal. 



In conclusion, I have to express my thanks, first to the 

 University of Cambridge and to the British Association, who 

 granted me the use of their tables at Plymouth ; next to 

 Dr. E. J. Allen, Director of the Marine Biological Laboratory 

 at Plymouth, who in the most whole-hearted and generous 

 manner placed the resources of the laboratory at my dis- 

 posal ; then to ray friend and colleague, Mr. J. Simpson, 

 B.Sc, Demonstrator of Zoology in McGill University, to 

 whose skill I owe a large proportion of the drawings which 

 illustrate this paper; and lastly to my wife, who also assisted 

 with the more complicated drawings, with the text-figures, 

 and with the general revision of the text. 



List of Wokks referred to in this Paper. 



N.B. — It lias not seemed to me desirable to encumber tliis list witli 

 references to works dealing willi groups of animals other tlian the 

 Ecliiiiodcrms, such as that of Lang on the TurbeUaria, or AVillcy on 

 Ctenoplana, etc., since the facts referred to have been embodied in 

 text-books and are the common properly of all zoologists. "Woltereek's 

 recent paper forms the sole exception. 



1. Agassiz, L. — "Selections of Embryological Monographs, II, Echino- 



dermata," *Meni. Mus. Comp. Zool. Harvard.,' vol. ix, pt. 2, 18S3. 



2. ArosTOLlDES, N. C. — "Anatomic et. developpcment des Ophiures,'" 



'Arch. Zool. Exi>./ vol. x, 1SS2. 



