PROTOZOA 



27 



it is perhaps in this respect, as well as in restriction of function, that 

 the cells of metazoa differ from protozoa. 



From the fact that, in many cases at least, the trophochromatin is 

 periodically destroyed and replaced, and from further facts which we 

 shall cite in discussing the significance of conjugation, it would appear 

 that trophochromatin, or some part of the protoplasm associated with 

 it, in the course of its regulative activity eventually becomes effete 

 and is replaced from the idiochromatin, which is not liable to that 

 fate. Perhaps the possession by protozoa of the facility for this re- 





Fig. 21. Nuclear phenomena in protozoa. A, Extrusion of the germ nucleus 

 froin the somatic nucleus in Gregarifia cimeata before gamogony. The somatic 

 nucleus will break up and disappear. B, Extrusion of the substance of the 

 endosome from the gamont of Eimeria schubergi, the germinal part of the 

 nucleus remaining in the centre of the body. C, Mitosis in Opalina ranarinn, 

 megachromosomes in anaphase in outer part of nucleus, microchromosomes 

 in metaphase internal to them. A, after Milojevic; B, after Schaudinn; 

 C, after Tonniges. 



placement, and the lack of such facility in the body cells of metazoa, 

 is the explanation of the fact that protozoa are not subject to the 

 "natural death" which eventually overtakes the body of a metazoon. 

 The loss of trophochromatin during the formation of gametes is 

 not to be confused with the reduction division of maturation. Reduc- 

 tion divisions, however, have been seen in members of all classes of 

 the Protozoa, and it maybe suspected that a process of this kind occurs 

 in all species in which there is syngamy. Such divisions are sometimes 

 {Actinophrys, etc.) strikingly similar to those of the Metazoa, but in 

 other cases {Paramecium, etc.) are peculiar. The reduction division 



