1897.] Embryology. 85 
cleaving cells are of this nature and not due to actual threads. That 
radiations may be formed in various preparations of soap-suds and 
mixture of white of egg and gelatine is shown by careful figures and 
by diagrams and the similarity of such artificial radiations to cell 
radiation demonstrated. Here a contraction of a central body, as an — 
air-bubble, suggests the way in which the centrosome may act. 
In elucidating the phenomena of cell division on the basis of a foam 
structure the author takes the figures given by Ziegler for sea-urchin 
and nematode as a norm. In these eggs the nucleus and the attraction 
spheres undergo very marked changes in size while the radiations in the 
protoplasm outside the nucleus quickly grow long and then short. 
These rhythmic changes of size and distinctness lead to the following 
assumptions, 
The centrosome absorbs liquid from the surrounding cytoplasm and 
then concentrates it into smaller bulk than it formerly occupied. The 
nucleus swells from absorbtion of liquid. The detailed application 
of these assumed factors to the phenomena of cell division cannot 
well be given in the bounds of an abstract and must be sought in the 
original. The author there sets forth how the absorbtion of liquid by 
the centrosome will lead to the formation of radiations, asters, as well 
as to the removal of yolk bodies, ete. from the neighborhood of the 
‘centrosome. The final division of the centrosome is brought about only 
in consequence of the swelling of the nucleus. This body removes liquid 
from the regions not affected by the centrosomes and this removal of 
liquid will cause a strain which may be represented as a system of 
‘curves concentric with the nucleus. Where the centrosome lies the cyto- 
plasm is already less liquid, more viscid, while on the opposite side of 
the nucleus it is most liquid. 
The removal of liquid from lines of alveoli causes the alveoli to become 
‘smaller and thus the rows exercise a pull upon the region of the centro- 
some. This pull of the alveolar material eventually parts the centro- 
‘some and draws the halves asunder. As the rows of alveoli that sur- 
round the nucleus are the longest their contraction under continued loss 
of liquid to the nucleus will lead to the separation of the centrosome 
halves till they reach the poles of the nucleus. 
The observed second increase in size of the centrosomes follows this 
period of nuclear swelling and leads to the formation of new sets of 
radiations. These radii, pr lines of alveoli, now reach to the cell wall 
and exert a pull upon it as liquid is taken in from the alveoli to the 
‘centrosomes. As the rows of alveoli become most viscid near the cen- 
trosome a more liquid region is left in the equatorial plane and here the 
