PROTOZOA IN GENERAL 



85 



cleus. The former is believed to preside over the nutritive functions of 

 the cell, the latter is active in cell division and transmits hereditary 

 characters. This significance of the two seems borne out by the fact 

 that after conjugation the old macronucleus disappears and a new one is 

 formed from a micronucleus, which insures agreement in the hereditary 



Adoral membranel l_e 



,Oral cilia 



Neuromotor 

 center 



Dorsal 

 membranelle 



Contractile 

 vacuole 



Macronucleus 



Micronucleus 



Ectoplasm 



Contract! /e_ 

 vacuole 



Cuticle 



Mouth 

 opening 



Oral cilia 



Adoral 

 membranelle 



'Esophagus" 



Myonemes 



Skeletal lamina 



Endoplasm 



caecum 



Rectum ' 



Anus ' 



Fig. 31. — Diplodinium ecaudatum Fiorentini. {After Sharp, in Univ. Calif. Pub. 

 ZooL, vol. 13, and by the coi/rtcsy of University of California Press.) An infusorian found in 

 the stomachs of cattle, to illustrate the extreme of intracellular differentiation as exhibited 

 by protozoans. Somewhat diagrammatic, and a composite based upon the study of actual 

 longitudinal microscopical sections of preserved animals. X 750. The black ring around 

 the esophagus, the connection from it to the neuromotor center, and the solid black areas 

 at the bases of the membranelles form the neuromotor apparatus. 



character of the two nuclei. In many cases chromosome formation has 

 been observed in the division of Protozoa, but in other cases it has not. 

 Some Protozoa, both flagellates and infusorians, show great special- 

 ization within the cell, and parts called cell organs, or organelles, are set 

 aside for certain functions. This phenomenon is called in general, 

 differentiation, and, since it occurs here within the cell, it is termed 

 intracellular differentiation. Such parts are contractile strands of proto- 

 plasm called myonemes, which correspond to muscles in higher animals; 

 conducting strands and coordinating centers, which perform the func- 



