450 EDWIN S. GOODRICH. 



ordinary leucocytes are assumed by the luematocytes in Gl. 

 siphouostoma, and to a lesser extent in Gl. unicornis. 



We can now return to the study of the function of the 

 nephridial sac. 



In the large species Gl. unicornis the nephridial sac is 

 always more or less filled with a mass of cells (figs. 3^ 8, 16, and 

 26), consisting of some hsematocytes and a large number of 

 amoeboid cells. luGl. sip bono stoma the cells in the nephri- 

 dial sac are almost all amoeboid hsematocytes. These cells are 

 no doubt brought in by the action of the ciliated organ from 

 the coelom. They penetrate also into the csecum, but in fewer 

 numbers. In the sac are generally found masses of waste matter 

 in the form of concretions, brown or yellow granules, and irre- 

 gular aggregations, together with bits of chsetse and any other 

 particles which may occur in the coelom (figs. 7 and 25). 



Similar but smaller aggregations of waste material may be 

 found floating in the coelom, especially towards the posterior 

 end of the body ; they are either actually within or surrounded 

 by a number of amoeboid cells,^ which evidently move about as 

 scavengers, and eventually find their way either singly or in 

 masses into the nephridial sac. 



The accumulation of such waste materials in the nephridial 

 sacs gives these organs a brown or black colour in the poste- 

 rior region of the body. The waste materials do not as a rule 

 penetrate into the caecum.^ 



Experimental proof of the account given above is afforded on 

 examining specimens which have been injected with powdered 



' I can confirm Cuenol's observation tliat in such cases the leucocytes 

 secrete a cliitinous substance round tlie foreign body, apparently as a protec- 

 tive measure. For instance, a broken piece of cbseta will be found with the 

 jagged ends covered over with concentric layers of secreted substance. 



2 The ciliated organ has already been described as producing a current 

 from without inwards ; occasionally, however, the action of the cilia appears 

 to be reversed, leading from the caecum outwards. The whole mass inside 

 the sac is sometimes seen to rotate, and it is possible that this is the normal 

 action of the cilia in the living worm. When the nephridia are dissected out 

 and placed on a slide under a cover-slip they are naturally subject to pressure, 

 which would be sufficient to impede the rotation. 



