426 ANN BISHOP 



of different vacuoles varies, which seems a very improbable 

 hypothesis. 



These vacuoles, present in the meganucleus during conjuga- 

 tion, are not to be associated in any way with the vacuoles 

 inside the larger ' macrosomes ' of a normal meganucleus. The 

 former were found in the interstices of the granular structure 

 and represent a vacuolation of the nuclear sap ; whereas the 

 latter appeared within the substance of the ' macrosomes '. 

 Although small macrosomes were always present in the mega- 

 nucleus of conjugants, no large nor vacuolated ones were ever 

 seen in the degenerating meganuclei of conjugants. It is 

 almost unnecessary to remark that this does not mean that the 

 presence of large vacuolated macrosomes can never be coin- 

 cident with conjugation, but merely that, in the comparatively 

 small number of conjugants that have been studied, they 

 have not been present. However, if the vacuolated-macrosome 

 condition is to be regarded as being caused by an unknown 

 factor in the culture, it may be that this same factor is not 

 suitable for inducing conjugation. 



No further visible changes took place in the meganucleus 

 until after the separation of the conjugants. 



In newly separated exconjugants the fragments of mega- 

 nucleus were present and stained as intensely as in conjugants. 

 These fragments contained vacuoles, as did those in the con- 

 jugants. In preparations made at a slightly later stage the 

 vacuoles had become more pronounced and now bulged out- 

 wards greatly. In some specimens they appeared to have 

 burst, for circular cavities could be seen in the fragments of 

 meganucleus. 



Absorption of the old meganucleus took place during the 

 first few days subsequent to separation. Gradually the frag- 

 ments took up the stain less intensely, and often a clear space 

 could be seen in the cytoplasm surrounding them. Not all 

 the fragments were absorbed at the same time. Complete 

 absorption of the meganucleus did not take place until the 

 rudiments of the new meganucleus had attained to a con- 

 siderable size (PI. 22, fig. 6, L. and A. A.). 



