MAUPAS'S EESEAROHES ON CILIATE INFUSORIANS. 605 



two gametes is the male or migratory pronucleus, the other 

 the female or stationary pronucleus. In stage E each 

 male pronucleus crosses over the other at the point of contact 

 of the gametes, and fuses with the female pronucleus of the 

 other gamete : the copulation in this species takes place in 

 the resting stage of the pronuclei. Each conjugate has now 

 a " copulation -nucleus," which we letter Z. 



„ o E 



V ^ 1 D 



m' m' B 



V : 



^ A 



Fig. 1. — Schema of nuclear processes in a conjugating Ciliate, from the first 

 division of the micronucleus (fi) to the formation of the conjugating 

 pronuclei (ju^s, /x^m). The arrow indicates the path of the migratory 

 pronucleus ; a bar is placed above the rejection nuclei. The dotted lines 

 separate the successive stages, marked by capital letters at the right 

 hand. 



The first mitosis, stage F, takes place in the front of the 

 body, but the nuclei Z^ pass to the hinder half to divide again 

 in stage G. By the elongation of the connective tubes in the 

 dispirema stage, G-, two of the nuclei Z^ pass into the 

 anterior end and become meganuclei ; and their respective 

 sisters pass to the hinder end and become the microuuclei of 

 the offspring of the first bipartition. 



Separation takes places in the stage Hg ; and young excon- 

 jugates seem to have neither mouth, gullet, nor frontal pro- 

 minence : from three to eight days elapsing before the mouth 

 forms afresh and feeding recommences; and from eighteen to 

 twenty-four hours more until the first bipartition. Before 

 this takes place the micronuclei move up and place themselves 

 beside the meganuclei ; one set goes to the fore, the other to 

 the hinder half of the body ; while a second contractile vacuole 

 appears in the front half. Transverse fission then takes place. 



