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. 
Coutiére 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 
larve. 
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. 
Fia. 9.—Developing eggs of Thompsonia. 1000. 
A. Young egg cell. D. Beginning of gastrulation; micromeres have 
B. Oocyte nucleus has come to lie excen- divided; macromeres undivided. 
trically owing to the development of E. Development of gastrulation; appearance of 
yolk (in black globules). vacuoles in the protoplasm of the macro- 
C. Four-cell stage: two micromeres meres. 
(unshaded) and two macromeres F. Gastrulation complete; macromeres have 
(shaded) containing the yolk. 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 
