132 J. J. LISTER. 



spheric forms, whose large nuclear elements are so strongly 

 contrasted, and in both young and old specimens. 



In favour of the view that they are food stuff are the facts 

 that they are always most abundant in the terminal chambers, 

 through which the greater part of the food taken in must pass 

 before it is elaborated into protoplasm, and that, as above stated, 

 they are to a large extent absent from specimens kept under 

 conditions unfavourable to nutrition. 



In the Infusorian Balantidium entozoon (Ehr.), which in- 

 habits the rectum of the frog, bodies which appear to be of a 

 similar nature are often present (fig. 4, a and h). In prepara- 

 tions (made in March) killed with osmic vapour, and stained with 

 picro-carmine, the macro-nucleus is deeply stained, and what 

 appears to be the micro-nucleus may generally be detected lying 

 in a depression in it. In some specimens no other stained bodies 

 are present, but in most cases numbers of round bodies with a 

 deep red stain are thickly scattered through the protoplasm. 

 They vary in size from 1 to 5 /u. or more in diameter, and while 

 many are uniformly stained, in others darkly stained bodies are 

 seen to lie in a clear or granular matrix (fig. 4 h). 



Considering the quiescent condition of the macro-nucleus 

 and the micro-nucleus in these specimens, the inconstant oc- 

 currence of the bodies, and the variety in size and constitution 

 which they present, it appears impossible to entertain the view 

 that they are nuclear, while the hypothesis that they are 

 formed in the elaboration of the food material presents no 

 difficulty, and is in accordance with other observations. 



Miss Greekwood (13) has described in the endoderm cells 

 of Hydra certain " nutritive spheres," which take a pink stain 

 with picro-carmine, and which, as the name given to them 

 implies, there is good reason to believe are formed in the 

 metabolism of the food materials. 



On these grounds I regard the stained bodies in question 

 met with in Polystomella as nutritive in nature, formed, that is 

 to say, in the elaboration of the food. 



It must, however, be stated, that I am unable by the methods 

 which I have hitherto employed to distinguisli them from the 



