464 PROTOZOOLOGY 



strands to which chromatin granules are attached; in stomach of 

 salmonid fish. One species (Davis, 1926). 



S. salmonis D. (Fig. 198, d, e). Sluggish amoeba; 10-25/* in di- 

 ameter; 1 to several nuclei; multiplication by binary fission; nuclear 

 division amitotic. Cysts are said to be more abundant than tropho- 

 zoites and their appearance seems to be correlated with the amount 

 of available food; cysts spherical, 15-35/t in diameter; cyst-mem- 

 brane thin and nuclei vary from 3 to many; during encystment, 

 chromatin bodies of trophozoite become collected in several masses 

 which then break up and each chromatin grain becomes the endo- 

 some of newly formed nucleus; cyst contents divide sooner or later 

 into 4-11 multinucleate bodies and the whole increases in size; 

 finally cyst-membrane disintegrates and the multinucleate bodies 

 become set free. Trophozoites are said to occur in the mucous 

 covering of stomach of host fish; cysts occur in both stomach and 

 intestine. Aside from the loss of certain amount of available food, no 

 pathogenic effect of the amoeba upon the host fish was noticed 

 (Davis). 



Genus Hydramoeba Reynolds and Looper. Nucleus vesicular 

 with a large central endosome composed of a centriole (?) and 

 chromatin granules embedded in an achromatic mass, achromatic 

 strands radiating from endosome to membrane; a ring made up of 

 numerous rod-shaped chromatin bodies in the nuclear-sap zone; 1 

 or more contractile vacuoles; apparently the most primitive para- 

 sitic amoeba; parasitic on Hydra. 



H. hydroxena (Entz) (Fig. 198, f-l). Parasitic in various species 

 of Hydra; first observed by Entz; Wermel found 90 per cent of Hydra 

 he studied in Russia were infected by the amoeba; Reynolds and 

 Looper (1928) stated that infected Hydra die on an average in 6.8 

 days and that the amoebae disappear in 4-10 days if removed from a 

 host hydra. More or less spheroidal, with blunt pseudopods; 60- 

 380/i in diameter; nucleus shows some 20 refractile peripheral gran- 

 ules in life; contractile vacuoles; food vacuoles contain host cells; 

 multiplication by binary fission. 



Ito (1949) found this organism in Hydra japonica, H. magnipapil- 

 lata, Palmathydra robusta, etc. in Japan. The trophozoites measured 

 26-2 10m long with a nucleus, 10-12/x in diameter. Early infection 

 occurs on the tip of tentacles and spreads to the body proper (Fig. 

 198, i-l). Since the tentacles remain contracted, the host hydra can- 

 not feed on food organisms and becomes "depressed." The amoebae 

 finally enter the coelenteric cavity and feed on the endoderm cells. 

 The host hydra becomes spherical. At25°C. death of the hydra may 



