PHAGOCYTOSIS IN PERIVESICAL FLUID OF ARBACIA. 145 



Dekhuyzen ( r oi) named them "thrombocytes" and compared 

 them to the blood platelets of the vertebrates. Cuenot, Geddes 

 and Dekhuyzen believed that when a clot was formed, these 

 cells fused with each other to form larger true plasmodial masses, 

 the cells of such a mass losing their identity. In order to check 

 this assumption, Geddes introduced colored granules into the 

 perivisceral fluid and observed that these colored granules weie 

 to be found in the large multinucleate masses which were formed 

 by the fusion of the amibocytes. Michel ('88) and Goodrich 

 ('19) claim that these cells do not form true plasmodial masses, 

 but do form aggregate plasmodia in which the cells retain their 

 identity and are in contact by their ectoplasmic surfaces alone. 

 Goodrich states further that these cells, instead of having a 

 number of delicate pseudopodia, are under normal conditions 

 provided with numerous flap-like membranous processes similar 

 to the undulating membranes of the Protozoa. These membra- 

 nous flaps when viewed in optical section have the appearance 

 of delicate pseudopodia. The membranous flaps are constantly 

 changing and when a drop of the perivisceral fluid is taken out 

 of the cavity and spread out on a slide, these cells clump together 

 if approximate to each other; if isolated, the membranes shrink 

 as the fluid evaporates leaving long, filamentous strands of 

 ectoplasm. 



The other types of amibocytes are larger than those just 

 described and contain colored or colorless globules. They also 

 have a relatively smaller nucleus and form blunt pseudopodia 

 when moving in the perivisceral fluid. Various functions have 

 been ascribed to these larger amibocytes. The red, green and 

 yellow material appearing in these amibocytes was said by 

 Cuenot to be stored fat; by McMunn to be a respiratory pigment 

 which he called by the non-committal name of echinochrome; 

 and by Ribaucourt this colored material was thought to be 

 excretory matter which was to be carried out of the body through 

 the ambulacral system by these amibocytes. They were all 

 agreed that these amibocytes were derived from the first type 

 of amibocyte by the inclusion of this material or by its precipi- 

 tation after absorption. Since these nutritional or nephritic 



