692 



SEXUALITY 



aggregations by the repeated addition of other individuals, as these col- 

 lide with those already united. In the course of an hour or so, the clusters 

 break down into conjugating pairs. A detailed account of this mating 

 reaction (Fig. 166) is given for P. bursaria by Jennings (1939a). 



The final pairs always consist of one individual from each of the two 

 caryonides. When animals of the two caryonides differ in size, each 

 pair consists of one large and one small animal. In P. bursaria (Jennings, 

 1938a) the two members of each pair differ in color when a normal green 

 culture is mixed with one made pale as a result of recent rapid multipli- 

 cation. 



When all possible combinations are made among a group of caryo- 

 nides, they are classifiable, on the basis of their reactions, into two groups 

 (Table 11); no two members of the same group will conjugate with 

 each other, but any two caryonides from different groups will. These 



Table 11: Results of Mixing Together Animals from Different 

 Caryonides of Stock F, Paramecium aurelia^ 



* -|- = conjugation; — = no conjugation. Data from Sonneborn, 1938a. The caryonides 2bl, 

 2b2, 3a2, 4bl, and 4b2 are of mating type I; caryonides lb2, 2al, 2a2, 3al, 5bl, and 5b2 are of 

 mating type II. 



