PHYSIOLOGICAL VARIATIONS IN PARAMECIUM 469 



tion. Paramecium may be accepted as a typical form of infu- 

 soria with which to test the value of Weismami's generalization, 

 and with the various observations and results of experimental 

 work on Paramecium in mind, a series of experiments was planned 

 to find out, if possible, what the conditions are which underlie 

 conjugation. In the course of the- investigation many other 

 points showing variations in the progeny of a single ex-con ju- 

 gant have been obtained. These indicate a phenomenon of the 

 nature of a developmental process in the life history of Parame- 

 cium and throw new light as well upon the old problems of age 

 and death in protozoa. The experiments were started in July, 

 1912, Miss Gregory sharing the work from November on. 



2. EXPERIMENTAL METHODS 



All experiments here described were each started with a 

 single-celled ex-conjugant of Paramecium caudatum. The most 

 striking results were obtained in connection with a race known in 

 the laboratorj^ records as the J series and this may serve to illus- 

 trate the methods employed in all cases, since tlxe methods have 

 been the same in all. 



A single pair, I- J of conjugating Paramecium caudatum was 

 isolated from a 'wild' pond culture on July 21, 1912; on the 22nd 

 the two cells, I and J, had separated and each was isolated in a 

 small watch glass with four drops of twenty-four hour hay infu- 

 sion as culture medium. On the 25th each of them had divided 

 twice, forming four cells each and from that time division was 

 fairly regular for the J series, while the I series became irregular 

 in division and weak in vitality, the entire race finally dying in 

 August. The first four cells formed after conjugation and re- 

 ferred to in the following pages as quadrants A, B, C, and D, 

 have particular importance for the reasons given in the preced- 

 ing section. This stage of development is important because if 

 there is any differentiation it is reasonable to suppose that it 

 should take place in this early period of development when by 

 division and metamorphosis the normal condition of the organism 



