PROTOZOA. 



I 49 



without any foreign matter. So far as we know, these simple 

 responses do not give evidence of special organs, but merely 

 represent a diffused protoplasmic irritability and power of 

 responding to stimuli ( 19, 20). 



FIG. 67. 



FIG. 67. Paramecium. i, transverse fission; 2-5, stages in conjugation. Lettering 

 as in Fig. 66. The meganucleus gradually disintegrates during the process and the 

 micronucleus by two successive divisions forms four micronuclei. Two of these dis- 

 integrate. One of the remaining micronuclei (n 3 ) in each animal passes into the 

 other Paramecium and unites with the stationary micronucleus (n 4 ), thus fertilizing it. 

 Later a new meganucleus is formed in each animal by the division of this body. 



Questions on the figure. What structures divide in the fission of 

 Paramecium? Which do not? Which is permanently represented in the 

 cell during conjugation, the micro- or the mega-nucleus? Which seems to 

 correspond most nearly to the ordinary nucleus of higher forms? What 

 really transpires in the act of conjugating? Compare this with more 

 elaborate figures in reference texts. 



194. Reproduction. In the Protozoa we discover methods 

 of reproduction which are to be looked upon as suggestions of 

 methods found in the Metazoa. Reproduction among the 



