CYTOPLASMIC INCLUSIONS 29 



body, but the region round the cytostome (peristome) may be modified 

 in various ways. There may be a ciliated groove leading to the cytostome 

 (Fig. 70), or a disc-like area upon which cilia are arranged in a spiral manner 

 (adoral zone of cilia) may be developed. These cilia are often continuous 

 with others within the cytopharynx. In the Peritrichida, like Vorticella 

 and Carchesium, the area round the cytostome is sunk in the form of a 

 funnel-shaped depression, the vestibulum, the opening of which may be 

 completely closed by contractions of the cytoplasm. Within the ves- 

 tibulum is found the cytostome itself, while the food vacuoles and con- 

 tractile vacuole also discharge their contents into it (Fig. 528). 



CYTOPLASMIC INCLUSIONS.— In association with the ingestion of food 

 and metabolism, granules, globules, and crystals of various kinds may 

 appear in the endoplasm. These are quite distinct from the partially 

 digested food in the food vacuoles, though they result from food meta- 

 bolism. Many Protozoa having affinities with the plants and possessing 

 chlorophyll are able to form starch, which occurs in the cytoplasm as 

 characteristic starch granules. They are commonly present in Euglena 

 and other similar forms. Another substance allied to starch is known as 

 paramylum. Fat globules are seen especially amongst the Radiolaria 

 within the inner capsule. They also occur in the marine flagellate 

 Noctiluca, and it has been suggested that they assist these organisms to 

 float. Doflein (1910) has noted that, in old cultures of Trypanosoma 

 rotatorium the flagellates may contain droplets of fat. Another substance 

 which is of common occurrence in the cytoplasm is glycogen, or a closely 

 allied substance which was called paraglycogen by Biitschli. These have 

 a strong affinity for iodine, which colours them an intense brown. Glycogen 

 is present in gregarines, certain ciliates, and very commonly in the encysted 

 forms of amoebae and flagellates (Plate II., p, 250). The iodophilic body 

 which occurs in the encysted stage of lodamceha hiUschlii has given rise to 

 its generic name. A substance which is of wide distribution amongst 

 the Protozoa is volutin. It is usually seen in living organisms as globules 

 of a greenish refractile material which takes a yellow colour in iodine. 

 Owing to the fact that it may stain deeply with chromatin stains, it has 

 often been regarded as chromatin. Some observers maintain that it is 

 actually a forerunner of chromatin. Volutin is often present in the 

 cytoplasm of trypanosomes and other flagellates, and appears as dark 

 red granules when they are stained with Romanowsky stains. It commonly 

 occurs in hsemogregarines and many Sporozoa, as also in amoebae and 

 ciliates. A substance which may be allied to volutin is seen in the 

 chromatoid bodies which are present in the cysts of some intestinal amcebae. 

 They occur so frequently in the encysted forms of Entamoeba histolytica 

 in the form of bars that they are highly characteristic of this species 



