18 



Papers from the Department of Marine Biology. 



So far as my own experience goes there is no sign of any organ which 

 can be called a testis nor of spermatozoa wandering through the 

 tissues. I think that probably Thompsonia is to be placed with Sylon 

 and Mycetomorpha as Rhizocephala which have substituted partheno- 

 genesis for hermaphroditism. 



Coutiere also seems to refer to this organ in speaking of a distally 

 situated growing point. I must confess myself unable to understand a 

 good deal of his description without the aid of figures. His conception 

 of the life-history of Thompsonia, moreover, leads him to see in the 

 visceral mass the abdomen of the Cypris larva and explain the prolifer- 

 ation here by the laws of growth observed in Annelids and Crustacean 

 larvae. 



DEVELOPMENT. 



The account which I give of the development of Thompsonia is very 

 incomplete, for the material in my possession illustrates only a number 

 of isolated stages. I have not been able to gather any information 

 about the maturation of the egg. 



A. Young egg cell. 



B. Oocyte nucleus has come to lie excen- 

 trically owing to the development of 

 yolk (in black globules). 

 Four-cell stage: two micromeres 

 (unshaded) and two macromeres 

 (shaded) containing the yolk. 



FIG. 9. Developing eggs of Thompsonia. X1000. 



D. Beginning of gastrulation ; micromeres have 



C. 



divided; macromeres undivided. 



E. Development of gastrulation; appearance of 

 vacuoles in the protoplasm of the macro- 

 meres. 



F. Gastrulation complete; macromeres have 

 divided once, so there are now four cells; 

 more generally there seem to be three. 



In the youngest external sacs the visceral mass is occupied by small 

 cells of uniform size. Amongst these there soon become differentiated 

 young oogonia which are rather larger than the remaining interstitial 



