148 



PROTOZOA 



the twenty-four hours at a temperature of 65-69 F. (Glaucoma 

 scintillans), so that in this period a single individual has resolved 

 itself into a posterity of 32; but such a rapid increase is 

 exceptional. At a minimum and a maximum temperature 

 multiplication is arrested, the optimum lying midway. If the 

 food-supply is cut off, encystment occurs in those species capable 

 of the process ; but when there is a mixture of members of 

 different broods of the same species, subject to the limitations 

 that we shall learn, conjugation ensues. Under the conditions 



ing.ncj 



Fig. 52. Paramecium caudatum, stages in conjugation, gul, Gullet ; mg.nu, mega- 

 nucleus ; Mg.nu, reconstructed meganucleus ; mi.nu, micronucleus ; Mi.nu, recon- 

 structed micronucleus ; o, mouth. (From Parker and Hasvvell, after Hertwig.) 



of Maupas' investigations he found a limit to the possibilities of 

 continuous fissions, even when interrupted by occasional encyst- 

 ment. The individuals of a series ultimately dwindle in size, 

 their ciliary apparatus is reduced, and their nuclear apparatus 

 degenerates. Thus the ultimate members of a fission-cycle show 

 a progressive decay, notably in the nuclear apparatus, which 

 Maupas has aptly compared to " senility " or " old age " in the 

 Metazoan. If by the timely mixture of broods conjugation be 

 induced, these senile degenerations do not occur. 1 In Stylonychia 



1 Calkins has recently found that the vitality within a cycle is rhythmical, 

 with alternations of more and of less frequent fissions, under the same set of 



