SPIROSTOMUM AMBIGUUM 



419 



show that the granular structure of the nucleus is quite normal. 

 The micronuclei, too, are normal (Text-fig. 5). 



The meganucleus next begins to contract and incidentally 

 to thicken. In some individuals contraction begins before the 

 lobation is completely lost, but in the majority of cases 

 the former is the normal method. In almost all individuals 

 the anterior part of the meganucleus remains in its normal 



Text-figs. 5, 6, 7, 8, and 9. 



position, and the posterior and middle parts contract towards 

 it in such a way that the almost completely contracted mega- 

 nucleus lies in the anterior end of the body (Text-fig. 6). Its 

 shape is still vermiform but much thickened and less than 

 a quarter of the length of the body. 



All the sections which have been studied of animals at 

 this stage show darkly stained granules irregularly dispersed 

 over a mesh-work. These meshes do not combine with stains 

 so strongly as do the granules. Preparations of stages inter- 

 mediate between the expanded and the anteriorly contracted 

 stages of the meganucleus show that the micronuclei move 



