512 Univeri.itij of California Publications in Zoologij [Vol.20 



The Motile Amoeba 



When examined in smears prepared in normal saline solution, 

 there is little or no apparent difference between the motile forms of 

 C. muris and C. decumani. The same type of hj'aline pseudopodial 

 formation (pi. 46, fig. 32) and of amoeboid movement are exhibited 

 and the amoebae inhabit the same parts of the digestive tract. The 

 food is similar and there is no evidence of a pathogenic effect upon 

 the rodent host. Cases of apparent cannibalism, however, have been 

 encountered in this species (pi. 46, fig. 30). A typical small amoeba 

 of this species is contained in a food vacuole within the larger amoeba. 

 The nucleus and food vacuoles of the ingested form are intact. Enda- 

 moeba coli has been shown to ingest cysts of E. dysenteriae (Wenyon 

 and O'Connor, 1917) and Lepage (1922) recorded a very interesting 

 instance of cannibalism in Amoeba vespertilio (Penard). In C. decu- 

 mani instances of binucleate motile forms have also been encountered 

 (pi. 46. fig. 31) by us in which the nuclei appear quite normal. 



When stained in iron-haematoxylin the nuclei of C. decumani 

 present an entirely different appearance from those of C. muris. The 

 nuclear membrane is heavier and more distinct and much more chro- 

 matin material is encrusted thereon in C. decumani than in C. muris. 

 In the former species, a distinct, more or less massed karyosome is 

 found in an exeentrie position. This may assume the form of a sphere 

 (pi. 46, fig. 30) or it may appear in the form of a crescent (fig. 32). 

 The karyosome may be surrounded by a light gray halo (figs. 30, 32), 

 or it may appear as an outstanding black sphere (fig. 31, upper 

 nucleus). Linin fibers connect the karyosome with the chromatin 

 material encrusted on the nuclear membrane, and small dots often 

 appear where these fibers cross. 



Encystment 



The process of encystment is a generalized one for parasitic 

 amoebae and nothing of importance differentiates the methods in C. 

 decumani and C. muris. Of great importance, however, is the differ- 

 ence in appearance of the contents of the cysts. The cytoplasm in 

 the cysts of C. decumani is more coarsely flaked than in C. muris, and 

 the chromatoidal bodies, while often arranged in sheaves of splinter- 

 like processes, as in C. muris (pi. 47, fig. 48), also commonly occur with 

 rounded ends, curved surfaces and as small spheres (fig. 50). Chro- 



