OPHIURA BREVISPINAi 



II. AN EMBRYOLOGICAL CONTRIBUTION AND A STUDY OF THE 



EFFECT OF YOLK SUBSTANCE UPON DEVELOPMENT 



AND DEVELOPMENTAL PROCESSES 



CASWELL GRAVE 



From the Zoological Laboratory of the Johns Hopkins University, 

 Baltimore, Maryland 



FOUR TEXT FIGURES AND THREE PLATES 



CONTENTS 



Introduction 413 



The egg 414 



Early development 415 



Blastula and mesenchyme formation 416 



The epigastric coelom and the organization of echinoderm eggs 419 



Yolk manipulation, a factor in development 425 



Correlation between yolk content of egg and duration of development 434 



Breeding hal^its of ojjhiura 440 



Summary and conclusions 443 



INTRODUCTION 



In a paper entitled 'Ophiura brevispina' which appeared in 

 1900 I pubhshed descriptions of the larva peculiar to this species 

 of brittle-star in various stages of its development, but, for 

 reasons stated in the paper, material was not then available 

 from which to describe an unbroken series of the stages in the 

 development of the larva, and the quantity of material repre- 

 senting some of the stages described and figured was not suffi- 

 cient upon which to base positive conclusions with reference 

 to the origin and fate of certain parts of the coelom. 



1 Ophioderma apparently has prior claim as the name of the genus and in 

 recent lists, viz., in the "Biological Survey of the Waters of Woods Hole and 

 Vicinity" by F. B. Sumner and others. Bull. Bureau of Fisheries, 1913, the name 

 of the species is given as Ophioderma brevispina (Say.) 



413 



