3. SYNAPTA VIVIPARA : A CONTRIBUTION TO THE MORPHOLOGY OF ECHINODERMS. 



BY HUBERT LYMAN CLARK. 



(Read November 3, 1897.) 



CONTENTS. 



1. Introductory G.'i (i. The development of the pentactula . . 63 



2. History and systematic position of Synapta vivipara 54 7. The development of the adult Synapta . . 68 



3. Distribution and habits 55 8. The anatomy of the adult 75 



4. Fertilization and segmentation of the egg . . 58 9. Conclusion 79 



5. Gastrulation and formation of the hydroeoel and 10. Literature 83 



coelomic vesicles |>1 11. Explanation of plates . . 85 



1. INTRODUCTORY. 



In February, 1896, through the kindness of Dr. W. K. Brooks, there were placed in 

 my hands for study a number of specimens of a small brown Synapta from Jamaica. In 

 their body-cavities there were numerous young ones in all stages of development, so that 

 an excellent opportunity was offered for working out the embryology. So interesting 

 did this prove that I gladly availed myself of the privilege of spending the months of 

 May, June, and July, 1896, at Port Henderson, Jamaica, in the marine biological labora- 

 tory of the Johns Hopkins University. For such a privilege I am under the greatest 

 obligations to the authorities of that institution. During those months, I studied the 

 segmentation of the egg and the early stages of development from living material and 

 obtained an abundance of preserved material for further investigations. Since my return 

 I have been engaged in a detailed study of the development and anatomy of the animal 

 under the direction of Dr. Brooks, and it gives me great pleasure to acknowledge the debt 

 I am under to him for his suggestions and help. 



The young were easily procured by cutting off the heads of the adults and thus 

 setting free the contents of the body-cavity. They could then be killed as desired, but 

 young taken from the body-cavities of preserved adults were fully as satisfactory for all 

 purposes. The best results were obtained by the use as a fixing agent of " corrosive- 

 acetic " (four parts corrosive-sublimate and one part glacial acetic acid), but excellent 

 preservation, especially for the adults, was secured by the use of picro-sulphuric or picro- 



