174 CYTOPLASMIC INCLUSIONS 



ently also associated with the food vacuoles, the refractive bodies, and so 

 forth, in a general transport function. The two groups are comparable, 

 but the granules of Ichthyophthirius perform only a part of the functions 

 assigned to them in Amoeba. It may be possible that the mitochondria 

 or beta granules of Amoeba include more than one type, but in view of 

 the detailed experiments which have been made on this form, this explan- 

 ation is hardly more than a possibility. 



This survey of functions which have a granular basis fails to reveal 

 any general uniformity, even in this restricted group of five Protozoa. 

 The most clear-cut case of two different mechanisms having the same 

 function is that of the segregation of reserve protein in Ichthyophthirius 

 and Opalina. No matter how broad the definitions are made, the fact 

 remains that the identical result is attained through the mediation of two 

 different cellular mechanisms — in the one case the mechanism is the 

 macronucleus, in the other it is strictly cytoplasmic, the segregation 

 bodies. The general concept of transport introduced by Doyle helps in 

 several cases to group apparently diverse functions within a single func- 

 tional concept; but here again none of Kedrowsky's published obser- 

 vations in the case of Opalina, nor my own observations in Ichthyoph- 

 thirius, would support this. The stored fat, paraglycogen, and proteins 

 merely decreased in size during encystment, and no intermediate bodies 

 aid in the redistribution of this material. 



The granules which are produced in a particular species are typical of 

 that species, but in other species the same function may be accomplished 

 by granules different in composition and relationships from those of the 

 first species, or the same function may be accomplished without the form- 

 ation of visible granules. The cell is not restricted in the accomplishment 

 of its functions by any system of universal and invariable cytoplasmic 

 components. 



The Continuity of Cytoplasmic Granules 



The failure to find evidence of universal cytoplasmic components by 

 the use of either composition or function as criteria, brings the discus- 

 sion to a much more general concept — the distinction between granules 

 as permanent organelles and as temporary reserve granules. This dis- 

 tinction can be traced back to Altmann's bioblast theory, but it has been 

 applied more recently in a modified and refined form to the mitochondria, 



