I48 REPORTS ON INVESTIGATIONS AND PROJECTS. 



other, so that their distal ends diverge less than before; then they move 

 back again, and so on, so that it appears that the cell pushes its way through 

 the water by means of the spines. 



The axis of the Gulf Stream is so far from the Tortugas that I could col- 

 lect there only rarely, although near the edge of the Stream there is a differ- 

 ent plankton, containing some of the rarer tropical forms, as Heterodinium, 

 species of Orinthocercus, Centrodinium, and large species of Peridinium. 

 In the immediate region of the Tortugas the water was quite shallow, and 

 this shallow coast water did not seem to afford suitable conditions for the 

 development of Peridinea. 



