CYTOPLASMIC INCLUSIONS 115 



localization of stainable materials or as a dense surface with less dense 

 centers, with the type of material the same in both places. 



The mitochondria in most Protozoa are fairly evenly distributed 

 through the cytoplasm, sometimes alone and sometimes associated with 

 various types of storage granules (see the discussion of function). 

 Faure-Fremiet (1910) found that if any localization occurs, the mito- 

 chondria tend to concentrate beneath the pellicle and occasionally around 

 the contractile vacuole. Horning ( 1927) extended these observations and 

 contends that mitochondria tend to concentrate near all membranes — 

 particularly around the food vacuoles during active digestion, beneath 

 the pellicle, and around the nucleus. Hall and Nigrelli (1930) criticized 

 Horning's identification of mitochondria, which was based largely on 

 dark-field observations, and showed that in Vorticella sp. the mito- 

 chondria are not associated with the food vacuole. Volkonsky (1934) 

 likewise rejected Horning's identification and showed that the granules 

 associated with the digestive vacuoles, in a large number of species, are 

 stainable only with neutral red. MacLennan (1936) found a similar 

 situation in Ichthyophthirius. In other Protozoa, however, the accumula- 

 tion of mitochondria near membranes has been confirmed. Mast and 

 Doyle (1935b) find that the mitochondria in Amoeba are occasionally 

 associated with the gastriole (food vacuole) and they were able to cor- 

 relate the association with the type and stage of digestion. They also 

 demonstrated an association with the contractile vacuole, confirming the 

 earher work of Metcalf (1910). Volkonsky (1934) found a small ag- 

 gregation of mitochondria around the food vacuole of Campanella and 

 Paramecium during the alkaline phase of digestion. Chatton and Grasse 

 (1929) showed that the filamentous mitochondria of Polykrikos tend to 

 accumulate near the pellicle, but instead of being parallel to the surface, 

 as in the ciliates described by Horning, are perpendicular to the surface. 

 Poljansky (1934) studied the changes occurring in the life cycle of Bur- 

 saria and found that the mitochondria of neutral individuals are uniformly 

 dispersed throughout the cytoplasm, but during conjugation (Figs. 28, 

 29) the mitochondria migrate to the periphery and form a definite zone 

 under the ectoplasm, and also around the micronuclear derivatives. The 

 chondriosomes again scatter during the growth of the macronuclear pri- 

 mordium. There seems to be neither universal nor permanent localization 

 of mitochondria near membranes, as is to be expected according to Horn- 



