48 



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 



Fig. 52. — Paramecmm caudatum, stages ia conjugation, gul, GuUut ; vir/.mi., niega- 

 micleus ; Mg.nu, reconstructed meganucleus ; mi.nu, niicronucleus ; Mi.nii, recon- 

 structed uiicronucleus ; o, mouth. (From Parker and Haswell, 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, wliich 

 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.^ In Stylonychia 



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

 vitli alternations of more and of less frequent tissiou?, under the saiiie set of 



