CONJUGATION AND ENCYSTMENT 341 



tion, especially when the cysts are dry. Calkins maintains that 

 it also functions as a rejuvenating process. Our results do 

 not, however, support this contention, as will be demonstrated 

 later. 



NATURE, CAUSE AND DURATION OF CONJUGATION 



Didinia that are about to conjugate divide in rapid succession 

 two or three times without taking any food. During this proc- 

 ess they become much reduced in size; the protuberance at the 

 anterior end bearing the mouth becomes considerably enlarged 

 and somewhat flattened; and when they are ready to conjugate 

 they have a peculiar jerky movement. Such individuals are 

 consequently readily recognized. They are usually found in 

 restricted areas in the cultures. In watch-glasses having numer- 

 ous didinia fairly uniformly distributed, I have repeatedly seen 

 numerous individuals, some conjugating and others ready to 

 conjugate, all crowded together in one small spot and none 

 elsewhere. Whether these aggregations are due to a restric- 

 tion of the preliminary processes to specimens in these regions 

 or to reactions in the preconjugants which result in the aggre- 

 gation^ I am unable to say. However, the fact that they tend 

 to remain in the region seems to indicate that they aggregate. 

 They probably secrete some sort of substance, when they are 

 in the conjugating state which acts on them as a weak acid acts 

 on paramecia, but which does not affect individuals which are 

 not ready to conjugate. The preconjugants in the restricted 

 area swim about rapidly, continuously stopping and turning in 

 various directions. Thus they frequently collide and if in these 

 collisions they chance to meet mouth to mouth, they usually 

 remain united owing to the adhesive character of the mouth 

 during this period. Frequently the mouth of the two conju- 

 gants is not directly opposite and occasionally three individuals 

 become united. Thus we see in these simple creatures, special 

 provisions which facilitate the unions of sexually mature indi- 

 viduals, provisions which are in some respects similar to those 

 found in the higher animals. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL, 23, NO. 2 



