568 W. BLAXLAND BEN HAM. 



do not pass. The cells die very nuicli more readily than in 

 the case of Octocha^tus, the amoebocytes soon forming a 

 "Plasmodium/' which Rosa has shown to be precedent to 

 death — one stage in degeneration. 



The method of observation of the fluid naturally varied 

 according to the object to be attained. For the investiga- 

 tion of the form and structure of the living elements a 

 hanging drop of the fluid was examined, the cover-slip being 

 supported on a ring or by some other means. In this way no 

 pressure on the cells occurred ; but the exposure to air, even 

 for a very brief moment, has — as Rosa has noted — certain 

 effects upon the cells, and I found it advisable to support one 

 side only of the cover, so that various depths of fluid could 

 be observed. The cells iu the centre being protected from 

 air, and at the same time being subjected to a minimum 

 pressure — if any, — were probably in a normal condition. 

 This method, too, allowed the use of various reagents. 



In fixing the cells I followed Rosa's suggestion of killing 

 them as they issue from the dorsal pore; by touching tlie 

 body with a drop of corrosive sublimate the fluid is dis- 

 charged and fixed. 



The Cellular Elements of the Fluid. 



The cells in the coelomic fluid are extremely abundant, the 

 plasma being, relatively, as little as in the blood of a frog, 

 for example. Thus the cells are crowded together, and seem 

 to exert a certain degree of mutual pressure upon one 

 another. 



I recognise four distinct kinds of cells (PI. 41, fig. 1), viz. : 



1. Amoebocytes. — Naked, more or less granular cells, 

 capable of thrusting out pseudopodia, in fact typical " leuco- 

 cyte-like " elements. 



2. Eleocytes. — Large lounded cells with a distinct 

 limiting pellicle, and incapable of forming pseudopodia. 

 The cytoplasm is filled with highly refringent oily globules. 



