152 



PROTOZOOLOGY 



some of the division-products of micronuclei by probably incor- 

 porating the old macronuclear material. In most cases this sup- 

 position is not demonstrable. However, Kidder (1938) has shown in 



S'd © © 



d e f g 



Fig. 57. Diagram showing the macronuclear regeneration in Parame- 

 cium aurelia (Sonneborn). a, an individual before the first division after 

 conjugation or autogamy, containing two macronuclear (stippled) an- 

 lagen, two micronuclei (rings) and about 30 disintegrating (solid black) 

 masses of the old macronucleus; b, two individuals formed by the first 

 division, each containing one macronuclear anlage, two micronuclei and 

 macronuclear masses; c, two individuals produced by the second division: 

 one (above) with the new macronucleus, two micronuclei and macro- 

 nuclear masses, and the other without new macronucleus; d-f, binary 

 fissions in which the two micronuclei divide, but old macronuclear masses 

 are distributed equally between the two daughters until there is one large 

 regenerated macronucleus and two micronuclei; g, division following f, 

 goes on in an ordinary manner. 



the encysted Paraclevelandia simplex, an endocommensal of the 

 colon of certain wood-feeding roaches, this is actually the case; 

 namely, one of the divided micronuclei fuses directly with a part of 

 macronucleus to form a macronuclear anlage which then develops 

 into a macronucleus after passing through "ball-of-yarn" stage simi- 

 lar to that which appears in an exconjugant of Nyctotherus (Fig. 85). 



