112 CYTOPLASMIC INCLUSIONS 



on these two types of investigation separately, with the result that in 

 many cases the morphological and functional studies of the cytoplasmic 

 granules have become separated. The one group emphasizes the classifica- 

 tion of granules into hard and fast categories of Golgi bodies, mitochon- 

 dria, vacuome and so forth, with little specific consideration of function, 

 while those engaged in functional studies tend to group all the granules 

 together or to devise entirely new systems, which hinder the comparison 

 of granules in several species. This review is an attempt to coordinate 

 these two angles of approach, so that both may contribute to our under- 

 standing of the role of the cytoplasmic granules in the cell. 



Since summaries are available of the characteristics of single groups 

 of granules, this review is not intended to provide an exhaustive catalogue 

 of the facts of any one group. Particular emphasis is placed on those 

 granules which have been described with sufficient completeness to fur- 

 nish evidence as to reactions, classification, and function, as well as their 

 relationship to other granules in the same cell. Specific directions on 

 standard techniques for demonstrating the various granules are avail- 

 able in the various books on microtechnique and histochemistry and so 

 are not described in detail here. The more recent publications will be 

 emphasized, since the specificity of methods has improved greatly and 

 summaries of the earlier papers are available in the works of Calkins, 

 Doflein-Reichenow, and others. The Protophyta have been omitted in 

 most cases, since their inclusion would complicate the picture unneces- 

 sarily. 



Mitochondria 



Undoubtedly many granules described in early cytological studies of 

 Protoza were actually mitochondria, but their status as a separate group 

 of cytoplasmic constituents in the unicellular organisms was not recog- 

 nized until the publication of the monograph of Faure-Fremiet (1910), 

 which emphasized the concept that mitochondria are universal, self -per- 

 petuating cytoplasmic constituents. 



The identification of mitochondria is not yet entirely satisfactory, 

 since it depends upon stains and fixatives of the lipoid component, a 

 material not restricted to mitochondria alone, or upon vital dyes which 

 are not as efi^ective in the Protozoa as in the Metazoa and which in certain 

 cases stain other organelles as well. Typical mitochondria are refractile 



