164 JUrjAN S. HUXLEY. 



this rim will press against the convexity of the ball and thus 

 be difficult to see; it is only in the early stages of extrusion 

 that its inner surface will form an angle with the surface of 

 the ball, and thus stand out. The pad of cytoplasm (p.) is 

 always seen at the anterior end of the ball vesicle, showing 

 that there can be no question of invagination. 



Retraction would then take place by the resorption of the 

 secretion ; while the ball seems to be kept in place by strands 

 from the ectoplasm (probable muscular layer), for this, and 

 this only, usually extends up the sides of the secreted fluid to 

 the ball vesicle (figs. 3, 5, 6). 



When fixation takes place, the condition of things looks 

 somewhat different (fig. 10), and there is an open communica- 

 tion from the ball to the space behind it. Very possibly the 

 cytoplasm at the neck is temporarily dissolved so as to leave 

 this passage-way for the food absorbed by the ball to pass 

 further into the substance of the animal. 



Finally, in association, the ball of one is extruded into 

 the cup of the other, and the cup then seemingly contracts so 

 as to hold the ball firm (fig. 9; text-fig. 1). It may be here 

 remarked that the free ball end in the couple in text-fig. 1 is 

 quite abnormal : it was pointed, and contained a pointed 

 cavity within it, but otherwise had none of the typical 

 structure. 



The cup-end also presents various difficulties. When 

 well formed its structure is simple enough, and has already 

 been described. But at other times the hollow cup may be 

 quite wanting, the body ending simply in a rounded end with 

 rather thick ectoplasm (fig. 12) ; or, more often, there are 

 numerous vacuoles beneath the cuticle (fig. 13), with some- 

 times an irregular aperture in addition (text-fig. 2). What 

 the meaning of these variations is, and whether the cup-end 

 can pass from one state to another, I fear I cannot say. 



It was from the presence of the cup that I ventured to call 

 this new genus Ganymedes, though the pedant will perhaps 

 maintain that this name should have been reserved for some 



