Nephridium o/'Nephthys c^eca, Fahr. 163 



(2) In specimens injected with powdered carmine (in sea- 

 water) the phagocytes laden with the grains collect here, 

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

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



Before describing the process of excretion some notice of 

 the coelomic fluid is necessary. 



Flouting free in the fluid are found two varieties of 

 cells : — 



(1) Cells of highly granular appearance (PI, I [I. fig.6),wliich 

 usually present a rounded form, but on careful inspsction 

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

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

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

 degeneration when loaded with excretoiy matter (Pi. til, 

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

 In almost every case they contain the characteristic yellow- 

 green matter, and in injected specimens are filled with 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. Tliey are iden- 

 tical in appearance with the corpuscles of the blo:)J. 



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

 follows : — 



Whenever a particle of solid excretory matter appears in the • 

 coelom it is immediately engulfed by one of the phagocytes. 

 This, when it has be:ome 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. 4, p), 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, tlie- 

 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 ingestion " 

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

 consecutively. 



11* 



