430 
R. T. Yoiing 
of the egg to imdergo maturation, which attempt is but one of the many 
evidences of a degeneration of initosis in cestodes, in correspondence 
with their parasitic habit and otlienvise generally degenerate condition. 
In the paper already referred to I have given many reasons for interpreting 
the yolk cells as such, and not as polar bodies, and in a more recent paper 
(1919 a) I have presented additional evidence in the fact that in Thysäno- 
sonia actinoides, where a yolk gland is wanting, this cell is also absent. 
Furthermore in such forms as RhyncobotMum, where the yolk gland is 
large, there are many of these ceUs attached to the ovum, forming a 
“compound egg”, and there is no cell among them distinguishable from 
the others as a polar body. 
There is yet another interpretation of these mitoses, alternative to 
either of those above given, which is that they are the first cleavage 
mitoses. Har>l\x attempts to differentiate between the maturation and 
cleavage mitoses in the following words. “The mitotic figure in maturation 
differs from the mitotic figure in Segmentation, in having a smaUer centro- 
some, and in the form of the chromosomes. The chromosomes in matu- 
ration are irregulär, while in Segmentation they are more definitely limited. 
The maturation spindle is always very long and one pole lies near the 
periphery of the cell. The Segmentation spindle may be long or short 
and may lie in almost any position.” To anyone familiai’ with the diffe- 
rences, not only in size, but also form of the cestode centrosome (or better 
centro-sphere), to which differences I have called attention in my previous 
paper, the uncertainty of an attempt to differentiate one mitosis from 
another by the size of their centrosonies will be at once apparent. The 
fomi of the clu'omosomes is perhaps an equally uncertain criterion. The 
cestode chromosome is at best a very unsatisfactory object of study, not 
only on account of its small size, but more especially because of its evi- 
dently very plastic nature, causing it to assume various forms under 
the action of fixatives, and frequently to unite with neighboring chromo- 
somes, producing not only marked differences in form, but also in number 
of chromosomes in different spindles. In my previous paper I have both 
described and figured such differences in munber, and anyone who is at all 
conversant with cestode cytology cannot fail to recognize the uncertainty 
attending any attempt to differentiate mitoses by means of either the number 
or the form of their chromosomes. In H.A.RiLA.N’s figures of the maturation 
spindles the chromosomes appeai' less numerous than in the cleavages, 
which is probably due to more or less fusion of the component elements, 
which may also explain their irregularity in the former; but that such 
differences are significant of a difference between the spindles containing 
