CONJUGATION IN PARAMECIUM 197 



degeneration and die. Similarly, if the food supply runs 

 short, the members of a swarm of Pararaecia become weak 

 and diminished in size ; but under normal circumstances the 

 onset of degeneration is arrested by conjugation. Prior to 

 conjugation the individuals move hither and thither in a rapid 

 and excited manner as if in search of one another. After a 



Stages in the conjugation of Paramecium caudatutn. A, Stage A, the micro- 

 nucleus in each gamete preparing for division. B, Stage B, the daughter 

 nuclei in each gamete dividing. C, Four micronuclei in each gamete. D, 

 Three of the four micronuclei are disintegrating ; the surviving nucleus in 

 each gamete has divided to form Q the male, and ^? the female pro- 

 nucleus. E, The male pronuclei crossing over, f, Conjugation effected ; 

 separation of the gametes and division of the combination nucleus. (After 

 Maupas.) 



while they come together in couples and conjugate. Two 

 individuals become attached together mouth to mouth, and 

 are closely united by fusion or, at any rate, the intimate union 

 of their ventral cuticular surfaces. The two conjugating 

 individuals or gametes are exactly like one another, though of 

 small size as compared with normal free-swimming forms. The 



