200 Lloyd Williams.- — Studies in the Dictyotaceae. 
curved rod-like form precludes that possibility-— it cannot, on the other 
hand, be regarded as a permanent cell-organ, for at several stages it 
disappears completely. At the same time, the comparison of normal with 
parthenogenetic segmentation strongly supports the idea that the egg after 
maturation is far less capable of giving rise to a new centrosphere than 
before. The unfertilized egg shows no indication of its presence, while 
in the fertilized ovum there is apparently only one, which subsequently 
divides to form the two centrosomes of the angular spindle. It is difficult 
to resist the conclusion that the antherozoid introduces into the egg 
something which enables it to form a centrosphere afresh. If this be 
correct, the imported substance can hardly be a centrosome, for no such 
structure can be recognized in the antherozoid before entry. 
With regard to the division of centrosomes, Mottier has described 
and figured the phenomenon in the early prophase of the second division 
of the tetrasporangium. I have never been able to satisfy myself that 
I have actually observed the splitting in the way that he figures it. In 
certain stages it is quite common to see the two chromosomes close to 
each other, and to find that during the later stages they travel farther 
from each other until the spindle, if already initiated, from being 
angular as at first, becomes quite straight or only very slightly curved. 
This occurs in the prophase of the first mitosis of the fertilized egg, in 
the newly formed daughter-cells of both tetraspore and oospore segmenta- 
tion, as well as in the case described by Mottier, but not in the newly 
formed nucleus of the tetrasporangium or in the first division of the 
tetraspore. 
The peculiarly irregular appearance of the membrane in the neighbour- 
hood of the centrosome in some stages tempts one to subscribe to the 
idea advanced by Mathews and others, that the centrosome is a liquefying 
enzyme, and that in virtue of this characteristic it may thus act not only 
upon the cytoplasm but upon the polar regions of the membrane also. 
This, however, is exceedingly doubtful, for not only have investigators 
failed to extract an enzyme from cells containing centrosomes, but in 
the parthenogenesis of eggs of Dictyota it has been shown that where the 
centrosome is absent the dissolution of the membrane is sudden and 
complete, and takes place at an early stage. 
3. The nuclear membrane. Whatever may be the structure and 
consistency of the membrane the phenomena just described support the 
hypothesis that its formation is determined by the metabolic processes 
going on in the chromatic mass. Evidently the reason for the formation 
of a number of nuclei in the parthenogenesis here described is that the 
chromosomes are too widely scattered, so that when a chromosome is 
isolated it directly or indirectly initiates the formation of a membrane 
round itself. Juel, in his paper on Hemerocallis , describes a stray chromo- 
