CHARLES B. METZ 



19 



specific. It occurs only between living and dead animals of complementary 

 mating type, never between animals of the same type. Following adhesion to 

 the dead animals and with the time schedule characteristic of normal conju- 

 gation, the living animals lose their mating reactivity, separate from the dead 

 animals and undergo the morphological and cytological changes characteristic 

 of normal conjugation (fig. 2). These changes include macronuclear breakdown 



sf'^'^'^l\ 



Fig. 2. Drawings of Paramecium 

 aurelia activated b}' contact with 

 formalin-killed animals of opposite 

 mating type. The living animals 

 were isolated as 'pseudo-selling 

 pairs' 248 minutes after mi.xing 

 living and dead animals. 



a, Micronuclei are in metaphase 

 of second meiotic division; macro- 

 nucleus is in 'skein' stage of break- 

 down, b, Second meiotic division 

 completed; macronucleus in skein 

 stage, c, Micronuclei are in meta- 

 phase of second meiotic division. 

 Note paroral cone, d, Micronuclei 

 are in telophase of second meiotic 

 division, e and /, These paramecia 

 are in same condition as in a. 



a 



d 



f 



and meiosis (59, 60). In brief, specific contact with dead animals of comple- 

 mentary type induces the primary physiological and cytological events of 

 conjugation in living paramecia. Thus the dead paramecia activate living 

 paramecia in the same sense that the spermatozoan activates the egg. This 

 action of dead paramecia upon living animals of complementary mating type 

 has been reported in Paramecium aurelia (60), P. calkinsi (61) and P. caudalum 

 (39). 



