PARAMECIUM CALKINSI. 



177 



be placed on this as the size relations vary in all races of all 

 species under different conditions. But I have never seen the 

 macronucleus of P. calkinsi as small as Stokes figured it for P. 



trichium. 



The micronuclear apparatus is almost identical with that of 

 P. aurelia and in marked contrast with that of the other species 

 (see Figs. 4 and 6) . In the first place, there are characteristically 



FIG. 5. 



FIG. 6. 



FIG. 5. 'Exploded' trichocysts of Paramecium calkinsi. 



FIG. 6. Micronuclear apparatus of Paramecium calkinsi. Left, from a total 

 preparation; right, from a section. Camera lucida sketches. 



two micronuclei situated in or near a slight depression of the 

 macronucleus. It has not been possible in every case to discover 

 two micronuclei but there can be no doubt that two are typical 

 of the vegetative cells. And, of course, as in all paramecia, the 

 position of the micronuclei varies considerably in different 

 individuals. Sometimes the macronuclear depression is on 

 one side and sometimes on the other side. Frequently there 

 are tw r o tiny depressions each with a micronucleus. Again, 

 the micronuclei may be at a considerable distance from the 

 macronucleus, though not in mitosis. 



In the second place, the relative size and the structure of the 

 micronuclei are essentially similar to those of P. aurelia. The 

 chromatin of the resting micronuclei is clumped to form an 

 endosome which is surrounded by an 'achromatic' layer 

 enclosed by a distinct nuclear membrane. 



