28 General Morphology of the Protozoa 



Certain subcuticular inclusions of Euglenida — the cortical globules of 

 Euglena archaeoplastidiata, which are expelled and stained brown in 

 iodine solution (22), and the rod-like bodies beneath the pellicular 

 striations of Peranema trichophorum (23) — also have been homologized 

 with trichocysts of ciliates. These inclusions are demonstrable by mito- 

 chondrial techniques in Peranema trichophorum (74). It has been sug- 

 gested (88) that such subcuticular bodies of Euglenida are merely 

 substances accumulated for the secretion of cyst membranes and similar 

 layers. 



Among the dinoflagellates, Polykrikos and Neynatodiniu^n contain 

 nematocysts resembling those of coelenterates (27, 136). The similarity 

 is so close that some workers have considered such nematocysts (Fig. 1. 

 14, A) to be foreign bodies ingested by the flagellates. However, this in- 

 terpretation is not supported by the regtdar occurrence of nematocysts in 

 certain species and their absence in others feeding on the same plankton. 

 The nematocysts lie free in the cytoplasm and nothing is known about 

 their possible discharge under natural conditions. 



THE CYTOSTOME AND ASSOCIATED 

 STRUCTURES 



The ingestion of solid food by organisms with a well developed 

 cortex usually occurs through a cytostome, which often opens into a 

 cytopharynx. The area leading to or surrounding the cytostome often 

 forms a specialized peristome in ciliates. Although a typical cytostome 

 and cytopharynx ("gullet") are to be expected only in holozoic organisms 

 with a well difl:erentiated body wall, interestingly similar structures occur 

 in certain amoebae (Fig. 1. 15, C, E, F) — Amoeba vespertilio and Hart- 

 manella sp. (99), and also Dientajnoeba fragilis (230), and Entamoeba 

 muris (227). Aside from their greater permanence, the cytostome and 

 cytopharynx of various flagellates represent little advance beyond the 

 condition seen in these amoebae. In ciliates, however, the peristomial 

 area may be equipped with an undulating membrane, a row of mem- 

 branelles, or differentiated zones of cilia. 



The peristome of Paramecium multimicromicleatum (Fig. 1. 15, G) 

 is lined with cilia, while the pharynx is equipped with a dorsal zone of 

 long cilia and the penniculus, a band of closely set cilia extending spirally 

 from an antero-dorsal origin to the ventral pharyngeal wall. Activity of 

 these specialized cilia drives particles into a zone of paraoesophageal 

 fibrils which are continued from the wall of the cytopharynx into the 

 endoplasm as the postoesophageal fibrils. When enough particles are 

 trapped, a food vacuole develops as a bulge in the dorsal wall of the 

 gullet. After separation from the gullet, the vacuole is guided into the 

 endoplasm by the surrounding postoesophageal fibrils which exert a sort 

 of "peristaltic" effect (147). The peristomial area, or "oral groove," serves 



