154 T row. — Observations on the Biology and 
trophoplasm with foam-structure. The nuclei moreover are 
preparing for division. The chief indications of this are the 
increase in size of the nucleus, the decrease in size of the 
central body, the increased prominence of the linin-threads, 
and the capacity for absorbing stains which is acquired by 
the nucleo-hyaloplasm. When the basal wall of the oogonium 
has made its appearance, these changes are very obvious, as 
may be seen by reference to Fig. 35, where it should be noted 
one nucleus is unusually large. 
The antheridia differ from the oogonia chiefly in size, form, 
and the absence of a central vacuole. The nuclei in the 
antheridia, however, undergo exactly the same changes as 
those in the adjacent oogonium, as may be seen in Fig. 35 
and succeeding figures. 
As development proceeds, the cell-wall of the oogonium 
thickens, the protoplasmic layer gets thinner, the vacuole 
gets larger, and the nuclei undergo very important changes. 
The fat-globules which give rise to such characteristic 
appearances in the fresh material are, of course, absent from 
all the preparations, their places being indicated by clear 
vacuole-like, more or less globular, cavities. It is not possible 
to distinguish between such cavities and the small true 
vacuoles. It is difficult, moreover, to determine the substance 
which fills these true vacuoles, whether it be hyaloplasm 
or cell-sap ; and so far as this research is concerned, it is 
impossible with the methods adopted. It may be regarded 
as certain, however, that in all stages of development from 
the formation of the basal wall to the development of the 
oospheres, the majority of the small clear spaces seen in the 
sections were occupied by fat-globules. 
The changes in the nucleus, however, were for us of chief 
importance, and much effort was exerted to get clear views 
as to the true nature of the various appearances observed. 
The first indubitable evidence of a division of the nucleus 
by an indirect method was furnished by finding nuclei, chiefly 
in antheridia, but sometimes in oogonia, in the spirem con- 
dition. About thirty nuclei, one of which is represented in 
