Opalina. 263 
sistent fibre which, at least in some instances, does not itself split 
seems to introduce insuperable difficulty into the schema. 
Catkins & Cunt (1907) describe splitting of the chromosomes in 
the maturation divisions of Paramaecium, with a clearness which 
leaves no doubt that this type of mitosis occurs in at least some 
of its divisions, and so is known among the Protozoa. 
Professor Boveri directed my attention to conditions in Ascaris 
megalocephala which seem similar to those in the telophases of mi- 
tosis in Opalina and which make it seem likely that the appearance 
of splitting in the chromosomes of Opalina during the telophases is 
not significant. In Ascaris the chromosomes are seen to be granular 
during the telophases, and the granules lie more or less distinctly 
in two rows at the edges of each chromosome, leaving the axes of 
the chromosomes lighter, as in Opalina. Van BENEDEN (1883, p. 343; 
1887, Plate V, Fig. 8) has referred to these conditions in Ascaris as 
showing a second longitudinal division of the chromosomes in the 
telophases, one having already occurred in the equatorial plate stage 
of mitosis. HrrpEnuatn, at the Anatomical Congress in Wiirzbure, 
1907, described an appearance of splitting in the chromosomes in the 
telophases of mitosis in cells of the skin of salamanders. Boveri, 
during the discussion of HrmpENHAIN’s paper, suggested that, inas- 
much as this appearence, when seen, is found in all parts of all the 
chromosomes, whatever their position may be. it cannot indicate a 
splitting of the chromosomes, but probably shows that the axes of 
the chromosomes in the cells of the salamander skin stain at this 
stage less deeply than the periphery. Chromosomes with unstained 
or faintly stained axes have since been interpreted by HarpenHain 
(1907) as having an axial linin fibril. The lighter axis of the chro- 
mosomes of Opalina during the telophases seems not to be due to 
the presence of an axial fibril of linin, but to the absence of  gra- 
nules at the axis and their presence at the edges of the chromosomes. 
The appearance of granular edges and a lighter axis in the 
chromosomes of Ascaris is said by Boveri to be transient, disap- 
pearing when the chromosomes branch to form the network of the 
resting nucleus, and not showing in the chromosomes when these 
reappear from the resting nucleus preparatory to the next mitosis. 
There is no reason to believe that the splitting of the chromosomes 
in the new mitosis is a reappearance of a double condition in the 
previous telophase. The appearances of doubling of the chromo- 
somes in the telophases seem quite similar in Ascaris and Opalina, 
and the condition in the cells of the salamander skin is somewhat 
