SYNGAMY AND SEX IN THE PROTOZOA 135 



and shows signs of enfeeble ment and " senility " or " depression " 

 a condition which, with continued isolation, reaches such a pitch 

 that the organism is unable to assimilate, grow, or reproduce, but 

 dies off inevitably unless conjugation with another individual 

 takes place. At a result of syngamy, the vigour of the race is 

 renewed, and the organisms once more grow and reproduce them- 

 selves actively until senility supervenes again. From these and 

 many other facts it would appear as if syngamy produced a 

 strengthening or re-organizing effect upon the organism, restoring 

 vigour and activity to vital functions that have become, as it were, 

 worn out and effete. 



One very important discovery has resulted from the experi- 

 ments of Calkins and Woodruff namely, that the necessity for 

 syngamy can be greatly deferred by change of environment. A 

 strain which has become senile and exhausted can be stimulated 

 and revived by a change of food. Even this remedy appears to 

 have its limits, however, a degree of exhaustion being reached 

 sooner or later which nothing can restore to its pristine vigour. 

 The animals may even reach a pitch of exhaustion so great that 

 they are unable to conjugate, but die off in a helpless manner. 

 Calkins explains such cases as due to the senility having affected 

 not only the vegetative, but also the generative chromatin ; pro- 

 ducing generative senility, which is incurable, instead of mere vege- 

 tative senility, for which syngamy is a remedy. Nevertheless, the 

 fact that the advent of senility and exhaustion can be deferred by 

 the stimulation of changed conditions is a very important discovery. 

 It must be remembered that the Ciliata are organisms of extremely 

 complex organization, and it is not unreasonable to suppose that 

 in such forms the work thrown upon the vegetative chromatin is 

 much heavier, and therefore the tendency to exhaustion much 

 greater, than it would be in an organism of simpler constitution ; 

 in such a form the stimulus of change of environment might defer 

 the advent of senility very greatly, perhaps even for an indefinite 

 period (Woodruff, 141).* This suggestion applies particularly to 

 parasitic forms, in which the organization is always greatly simpli- 

 fied, and in which change of environment from generation to 

 generation is inseparable from their mode of life. It would not be 

 surprising, therefore, if syngamy were found to be completely in 

 abeyance in a parasitic form of simple structure. 



It should be noted here that examples of syngamy being in 

 abeyance are not wanting even in higher organisms. An instance 



* In his most recent work on Paramecium, Woodruff (142) expresses the view 

 that " most, if not all, normal individuals have, under suitable environmental 

 conditions, unlimited power of reproduction without conjugation or artificial 

 Stimulation." Compare also Woodruff and Baitsell (143). 



