THE INFUSORIA 



193 



ism as in the Ciliata. Worked out first by Biitschli and Engelmann 

 in 1876, it has since been carefully studied by numerous observers, 

 and the conditions preliminary to conjugation, during, and subsequent 

 to it have been made known in a great variety of forms representing 

 all divisions of the class. Biitschli and Engelmann early recognized 

 that conjugation is necessary for continued life activity of the organ- 

 ism, and came to the conclusion, which has been fully confirmed by 

 subsequent observers, that conjugation is a process of rejuvenation or 

 a renewal of vitality, the need of which is shown by the reduced size 



Fig. 106. Diagrams to illustrate the division of Stentor rceselh. [JOHNSON.] 

 y, the vacuole ; A", the ring canal. 



and general degenerate condition of the organism prior to conjuga- 

 tion. Maupas ('89), in his classical work on conjugation among Infu- 

 soria, found that the number of generations which may be formed from 

 one conjugating period to the next varies with the species, but is 

 usually between three hundred and four hundred and fifty. He found, 

 furthermore, that certain conditions are necessary for conjugation. 

 These conditions are : (i) maturity of the organisms, i.e. forms which 

 have just conjugated will not again conjugate until after a certain 

 number of generations ; (2) partial lack of food, i.e. if plenty of food is 

 present, conjugation will not take place even though the individuals 

 are well along in degeneration ; (3) diverse ancestry, i.e. the conju- 

 gants must come from different ancestral conjugants. 



