General Morphology of the Protozoa 39 



senting the third condition, are refractile inclusions present in young 

 cysts in certain Endamoebidae. Little is known about the origin of protein 

 reserves. However, protein granules are extruded from the macronucleus 

 of Ichthyophthirius multifiJiis after the ciliates invade a host and begin 

 to feed (156). Similar achromatic bodies in the macronucleus of Blepha- 

 risma midulans also have been interpreted as protein reserves (239). The 

 chromatoid bodies of Entmnoeba histolytica on the other hand, are 

 formed by the coalescence of clear vacuoles which appear in the cytoplasm 

 (90). Dietary factors may influence the synthesis of protein reserves. Stor- 

 age of protein granules in Polytoma uvella, for example, is extensive in 

 a medium containing butyrate, but is much less noticeable with acetate 

 (220). 



Volutin granules, known in many Protozoa, presumably should be con- 

 sidered nitrogenous reserves (158). Although the term has been used 

 rather loosely, volutin may be considered metachromatic material which 

 is Feulgen-negative but is stainable by a modified technique which omits 

 preliminary hydrolysis (158, 188). The disappearance of volutin in try- 

 panosomes and haemogregarines after digestion with ribonuclease in- 

 dicates that the granules contain ribonucleic acid (5). Such granules are 

 resorbed in old cultures and during induced starvation of Polytoma uvella 

 (220); they accumulate during active feeding of Oxymonas dimorpha and 

 decrease in the motile phase (32), and are apparently a reserve food in 

 Pelomyxa caroUnensis (233). 



Crystalline inclusions are found in various species. The crystals of 

 Amoeba proteus apparently contain amino acids, presumably derived 

 from digested food (165, 166), but the composition of such inclusions in 

 many other Protozoa remains to be determined. As traced in Paramecium 

 bursaria (232), crystals accumulate during holozoic feeding and then 

 disappear gradually as the supply of bacteria in the culture is exhausted 

 and the ciliates become increasingly dependent upon their symbiotic 

 algae. 



Chromidia 



Originally, chromidia were defined as granules derived from the 

 nucleus. Certain "generative" chromidia were considered extranuclear 

 chromatin granules with a potential ability to form aggregates and de- 

 velop into nuclei. In other cases, extrusion of chromidia from the nucleus 

 was believed to be a means of restoring a normal nucleo-cytoplasmic ratio. 

 In more recent literature, a variety of inclusions — probably including 

 mitochondria, volutin granules and protein granules ("albuminoid re- 

 serves") — have been referred to as chromidia. Since the older chromidial 

 theories are no longer accepted, and the identities of the more modern 

 "chromidia" are so varied, it seems advisable to drop the term as a 

 designation for cytoplasmic inclusions of Protozoa. 



