112 



broad, bands-hapecl pseudopodia by which they become united. At this 

 time they form a more or less compact mass. This passes later into 

 the resting condition as described. 



The chromosomes are at all times granular, though during the mi- 

 gration stages of mitosis these granules are usually less readily distin- 

 guished from the intermediate substance of the chromosomes. 



During and following the compact stage the chromosomes become 

 sharply differentiated into granular portions and homogeneous spheres. 

 The chromatin spheres vary in size and number in different nuclei and in 

 different chromosomes. The granular portion consists of a weakly-staining 

 matrix (I believe usually in the form of a thin plate) containing darkly 

 staining granules of slightly different sizes, the smallest being the size 

 of the ordinary granules at the nodes of the linin net. The chromatin 

 spheres disappear (at least as such) from the nucleus. Perhaps they pass 

 into the cytoplasm through the ends of the nucleus, at the points where 

 the nuclear membrane broke in a previous division. (Compare the de- 

 scription of the cytoplasmic spherules, given later.) At no stage seen 

 do the chromosomes entirely disintegrate into granules. The plates of 

 faintly staining chromatin uniting them into groups can always be dis- 

 cerned even in the most diffuse stages. It is not well here to attempt 

 any discussion of the significance of the chromatin spherules. 



The nucleolus, a true plasmosome, has not as yet been carefully 

 studied. 



The striated condition of the dividing nucleus passes into the net 

 and foam structure of the »resting« nucleus by the restrengthening and 

 new formation of lateral branches of the linin and chromatin fibrils. 



Opalina caudata. 

 This species closely resembles 0. intestmalis^ except that it has 

 six instead of eight chromosomes. 



All the phenomena so far discribed , excej)t those of the linin net 

 and the lateral branches of the chromatin fibrils, have been seen in the 

 living nuclei and cannot be artifacts. 



The much smaller size of the nuclei and the greater number of the 

 chromosomes in 0. ranariiin.^ 0. dimidiata^ 0. obtrigona and 0. xelleri 

 render these species much less favorable for study. 



Cytoplasmic spherules. 



The cytoplasm of Opalinai^ divided into ectosarc and endosarc. Both 

 contain in the vacuoles of their foam-like plasma very numerous sphe- 

 roidal or more usually ovoid bodies (fig. 4). I believe that all individuals at 

 all times of year contain these and that in cell division they are handed 



