24 PROTOZOOLOGY 



brown chromatophores, which Uvc in Foraminifera and Radio- 

 laria, and certain algae belonging to Chlorella ("zoochlorellae") 

 containing green chromatophores, which occur in some fresh- 

 water protozoans, such as Paramecium bursaria, Stentor amethys- 

 tinus, etc., are looked upon as holding symbiotic relationship with 

 the respective protozoan host. Several species of the highly in- 

 teresting Hypermastigina, which are present commonly and 

 abundantly in various species of the termite and the woodroach 

 Cryptocercus,have been demonstrated by Cleveland to digest the 

 cellulose material which makes up the bulk of wood-chips the 

 host animals take in and to transform it into glycogenous sub- 

 stances which are used partly by the host insects. If deprived of 

 these flagellates by being subjected to oxygen under pressure or 

 to a high temperature, the termites lose the flagellates and die, 

 even though the intestine is filled with wood-chips. If removed 

 from the gut of the termite, the flagellates die. Thus the associa- 

 tion here may be said to be an absolute symbiosis. 



The parasitism is an association in which one organism (the 

 parasite) lives at the expense of the other (the host). Here also 

 ectoparasitism and endoparasitism occur, although the former 

 is not commonly found. Hydramoeha hydroxena (p. 321) feeds on 

 ectodermal cells of Hydra which, according to Reynolds and 

 Looper, die on an average in 6.8 days as a result of the infection 

 and the amoebae disappear in from 4 to 10 days if removed from 

 a host Hydra. Costia necatrix (p. 264) often occurs in an enormous 

 number, attached to various freshwater fishes especially in an 

 aquarium, by piercing through the epidermal cells and ajipears to 

 disturb the normal functions of the host tissue. Ichthyophthirius 

 multifiliis (p. 504), another ectoparasite of freshwater fishes, goes 

 further by completely burying themselves in the epidermis and 

 feeds on the host's tissue cells and, not infrequently, contributes 

 toward the cause of the death of the host fishes. 



The endoparasites absorb by osmosis the vital body fluid, feed 

 on the host cells or cell-fragments by pseudopodia or cytostome, or 

 enter the host tissues or cells themselves, living on the cytoplasm 

 or in some cases on the nucleus. Consequently they bring about 

 abnormal or pathological conditions upon the host which often 

 succumbs to the infection. Endoparasitic Protozoa of man are 

 Entamoeba histolytica, Balantidium coli, species of Plasmodium 

 and Leishmania, Trypanosoma gambiense, etc. The Sporozoa, as 



