yo 



THE INVERTEBRATA 



longitudinal ridges on the ectoplasm, forms spores endogenously in 

 the unencysted condition, and does not normally feed on diatoms, 

 which form a great part of the food of A. duhia. 



Entamoeba (Figs. 55, 56). Parasitic amoebae; without contractile 

 vacuole. Reproduction during most of the life history is by binary 

 fission. Finally encystment takes place and in the cyst the nucleus 

 divides several times. The cysts pass out of the host and infect a new 



^■f£-..5>;.*" Jia-tf'- '..'<?-!i' : 



^.VV'%^•lL-■<a•;^•:v^r.•£•i 



^ -St ..•,■■' - ■ - '> ■-'■' 



1^ 



><^- 



■\^^ 



-••'■•'''?; 



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

 teus. a^, Equatorial view of nucleus, a^, Polar view of nucleus, a^. 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. b^, 40 X 18. c\ 40 X 32. a*, maximum 4-5. b^, maximum 2-5. 

 ^3_^io^ maxima 10 to 30. 



individual, in which they are dissolved and set free their contents, 

 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 oc- 

 casionally abscesses of the liver and other organs, differs from E. coli 

 in having a distinct ectoplasm, in the central position of the karyo- 



