Xephriilium o/Xuphtliys c:«ca, Fnhr. IG3 



(2) In specimens injected witli powtleic'l caruiitit! (^in sea- 

 water) the pha<^ocyte.s ladiMi with the grains collect here, 

 forniing a prominent scarlet mass ; but only in one case have 

 I fouiul a carmine granule in the wall of the tube. 



Before describing the process of excretion some notice of 

 the coelomic fluid is necessary. 



Floating free in the fluid are found two varieties of 

 cells : — 



(1) Ctdlsof highly granular appearance(PI. III. ti^'.O), which 

 usually present a rounded form, but on careful iinp action 

 prove to be amoeboid. In some there is the appearance of a 

 firm ectosarc or cuticle, in others small bud-like outgrowths 

 occur, and in several cases I have found them in a state of 

 degeneration when loaded with excretory matter (PI. III. 

 fig. 8). These cells are tiie phagocytes already referred to. 

 In almost every ease they contain the characteristic yellow- 

 green matter, and in injected specimens are filled witli carmine 

 grains. 



(2) Oval cells of clear protoplasm (PI. III. fig. 7). At the 

 narrower end occurs a clear highly refractive nucleus. These 

 cells do not appear to be concerned in excretion, and I have 

 never observed any foreign bodies in them. They are iden- 

 tical in appearance with the corpuscles of the bloo 1. 



To sum up, the process of excretion appears to be as 

 follows : — 



Whenever a particle of solid excretory matter aj)pears in the 

 coelora it is immediately engulfed by one of the phagocytes. 

 This, when it has become sufficiently loaded, passes into the 

 neighbourhood of the ciliated organs, either by its own 

 amoeboid motion or by the agency of the currents raised by 

 the cilia. Here it is swept down one of the grooves, and joins 

 the little mass of its fellows raised against the barrier of the 

 nephridial tube. Partial degeneration now sets in, and the 

 phagocyte appears to bodily enter the protoplasmic wall of 

 the canal (PI. III. fig.-i,/>), carrying the foreign matter with it. 

 The latter then passes out either by the lumen of the canal, 

 assisted by the cilia, or by passing along through the wall 

 itself. 



The whole nephridium is in a state of constant motion, tiie 

 ciliated organ swaying up and down, the tube also moving" 

 upward and downward on the blood-vessels to a limited 

 extent. These movements no doubt facilitate the inge-ition 

 of refuse into the tube, bringing different parts of it into action 

 consecutively. 



II* 



