312 M. M. Mercaur 
extraction of the stain seems always to bring out the netted appear- 
ance in some of the discs (generally the larger and thinner ones) 
and not in others which seem more nearly normal. In Fig. 102 and 
103 each nucleus is seen to contain a central mass of granules 
whose later behaviour indicates that they are probably chiefly 
achromatic. Fig. 105 shows a radiate arrangement of these achroma- 
tic granules, the chromatin having gathered into a sphere which 
shows the characteristic netted appearance. Figs. 106—109 show 
that there may be one or two of these spheres. When two are in 
the same nucleus one may be much smaller (Fig. 107, a). In many 
of the figures, especially in Figs. 106 and 107, one sees that the 
center of each chromatin sphere is filled with a refractive body 
which does not stain with DenarireLp’s haematoxylin. The chromatin 
net lies like a cap partially, or almost completely, enclosing this 
central body. The presence of these referactive bodies in such 
intimate association with the aggregated chromatin recalls the for- 
mation of refractive spherules in the macronucleus or its fragments in 
Hoplitophrya and the possibly similar phenomena in Loxodes rostrum 
(JosEPH 1907), and gives a little more probability to the suggestion 
that in O. intestinalis and O. caudata the chromatin spherules after 
they leave the nucleus and reach the cytoplasm, may aid in the 
formation of the refractive spherules of the endosarc. Bovert (1907, 
see his plate XXIII) has described in degenerating nuclei of disperm 
Echinoderm larvae compound chromatin and refractive bodies very 
closely resembling those here described in the degenerating nuclei 
of O. obtrigona. 
Figs. 110 to 118 show a very interesting arrangement of the 
achromatic granules in the form of two polar groups with lines of 
granules connecting them and often with a more or less evident 
radiate arrangement of the granules around the polar groups. One 
or two of the netted chromatin spheres lie on the outer side of the 
granular spindle-fibres, at the equator of the spindle. Fig. 110 shows 
the chromatin sphere still adhering to the nuclear membrane. In 
Fig. 111 we see the two chromatin spheres withdrawn from the 
nuclear membrane and lying upon the spindle. The polar groups of 
granules, and the lines of granules composing the spindle, at first 
sight suggest comparison with a mitotic spindle with large polar 
centrosomes. It seems to me not improbable that they are essentially 
similar to the structures in some protozoan nuclei which have been 
regarded as spindle and centrosomes. (Compare R. Hertwie 1899, 
Paramaecium micronucleus; Scuaupinn 1894, Amoeba crystalligera; 
