20 



BIOLOGY OF THE PROTOZOA 



plete intracellular differentiations are present in the majority of 

 Infusoria, while many of the flagellates, notably the Trichonymph- 

 idse, have an almost equally elaborate make-up. In all such cases 

 the single cell is a complicated mechanism and the cooperating parts 

 have the same relation to the organism as a whole as do the organs 



Alar..- 



M ic--m 



c. v.- - - 



Fig. 2. — Diplodudum ecaudatum, a parasitic ciliate in cattle. A, anal canal and 

 defecatory vacuole; C. F., one of the two contractile vacuole!?; M, motoriuni with 

 fiber to circumpharyngeal ring; Mac, macronucleus ; Mic, micronucleus ; S, skeletal 

 layer. (After Sharp.) 



of a metazoon. Compared with an Amoeba froteu.s or other simple 

 rhizopod such complex organisms are highly specialized and show 

 the extent to which intracellular differentiation may be carried. 

 As Gurwitsch, Ilartmann, Dobell, and others have pointed out, the 

 applicati(ni (jf the term cell which designates a structural unit with 



