116 CYTOPLASMIC INCLUSIONS 



ing's theory that mitochondria accumulate at the intracellular surfaces in 

 accordance with the Gibbs-Thompson Law. Doyle (1935) suggests that 

 mitochondria tend to collect at regions of active interchange, since 

 he found that mitochondria are the only granules which flow out into the 

 pseudopodia of the foraminiferan Iridia. While this theory is attractive in 

 certain cases, it is difficult to see how this would apply to the concentra- 

 tions which occur in conjugating Burs aria. 



Mitochondria are more widely accepted as universal, permanent, and 

 self-perpetuating granules than any other cytoplasmic component, and for 

 this reason it is worth while to consider in detail the proof upon which 

 such statements rest. Rigid proof of this theory requires a demonstration 

 of mitochondria only, with, of course, a lack of evidence of any de novo 

 origin. Furthermore, it is obvious that proof of the continuity of any 

 cytoplasmic component cannot be based on a study of only one stage 

 in the life cycle, but must rest upon adequate studies of the whole life 

 cycle. 



Mitochondria have been identified in a multitude of Protozoa of all 

 groups by Faure-Fremiet (1910) and later authors, and as a result these 

 components are usually considered to be present in all Protozoa. How- 

 ever, recent evidence shows that this assumption is unjustified. An ex- 

 treme example is Trypanosoma diemyctyli, in which Nigrelli (1929) 

 was not able to demonstrate any pre-formed mitochondria, although 

 granules which satisfy the general criteria of mitochondria are induced 

 by exposure of the organisms to Janus green B. These induced granules 

 are not permanent, but disappear after about two hours. The marine 

 amoeba Flabellula is another species in which mitochondria are normally 

 lacking. Hopkins (1938b) found that the normal amoeba possessed no 

 granules which can be classified as mitochondria, but that when the 

 amoeba is disturbed in a variety of ways, granules are precipitated in 

 small pre-formed cytoplasmic vacuoles, the contents of which are nor- 

 mally a homogeneous fluid. After the recovery of the amoeba from the 

 disturbing conditions, the granules are resorbed. These temporary 

 granules possess the staining reactions of mitochondria, including the 

 ability to segregate Janus green B, and are the only granules in this 

 organism which can be classed in that group. As a contrast to these cases 

 of induced mitochondria, Kirby (1936) reports the experimental destruc- 

 tion of the mitochondria which are a normal component in the cytoplasm 



