AMOEBINA 65 



which divide into uninucleate young. The cysts must remain in a fluid 

 medium if they are to cause reinfection. Several species exist, occur- 

 ring in various vertebrates and invertebrates. E. coli is a harmless 

 commensal in the colon of man, feeding on bacteria, etc. E. histolytica 

 (= E. dysenteriae), a parasite which often causes dysentery and 

 occasionally abscesses of the liver and other organs, differs from 

 E. coli in having a distinct ectoplasm, in the central position of the 



'^i-^^-A 





Fig. 54. Amoebae. From Hegner and Taliaferro, after Schaeffer. A, A. pro- 

 tens, a^, Equatorial view of nucleus, a^polar view of nucleus. «^, Equatorial 

 view of nucleus in the folded condition often seen in this species, a^, Crystal 

 of the kind found distributed in the endoplasm of the species. B, A. discoides. 

 6\ 6^, Equatorial and polar views of nucleus. 6^, Crystal. C, A. dubia. c^,c^, 

 Equatorial and polar views of the nucleus. c*-c^^, Crystals and concretions. 

 Dimensions in microns : A, 600 in length. B, 450 in length. C, 400 in length. 

 a^, 46 X 12. 6^, 40 X 18. c^y 40 X 32. a*, maximum 4-5. b^, maximum 2-5. 

 c^-c^°, maxima 10 to 30. 



karyosome and in certain other features of the nucleus (Fig. 55), 

 and in forming only four, instead of eight, nuclei in the cyst. This 

 species breaks up by digestion cells of the intestinal epithelium and 

 other tissues, absorbs the soluble products, and ingests portions of 

 the destroyed cells and also red corpuscles. 



Pelomyxa (Fig. 57). Large, multinucleate species, living in, and 

 feeding by ingesting, the mud of stagnant fresh waters rich in organic 

 debris. The cytoplasm contains glycogen granules (see p. 15). 



Bi 5 



