II. The Cytology of the Gametophyte Generation. 187 
the thallus and those of the free, reproductive portions. For want of space 
this topic must be deferred for discussion in another paper. It may be 
pointed out that we have a provision here for the rapid elongation of the 
gametangial walls, for the early splitting of the lateral walls, and for their 
dissolution when the gametes arrive at maturity. It is evident that the 
basal cells have their walls of different chemical composition, and of more 
enduring character. 
When quite mature the degeneration of the apical walls and the 
increasing turgescence of the ovum causes the former to burst and to 
liberate the oosphere, which now lies a naked spherical mass of protoplasm. 
Fig. 19 shows a section through such an ovum. The nucleus now occupies 
nearly one-third of the diameter of the egg. It is surrounded by a zone 
of 4 kinoplasm,’ outside of which is the somewhat vacuolated cytoplasm 
with its numerous chloroplasts. In well fixed material these are generally 
oval or rounded, but when much contraction has taken place they are 
very narrow and elongated. At the periphery of the egg there is a zone 
of granular cytoplasm in which are embedded numerous intensely staining 
physodes. 
Very soon after liberation of the oospheres in a sorus the oogonial 
walls are completely dissolved, leaving only the basal cells, which are 
marked from the other surface cells of the thallus by their slightly 
greater width, and particularly by their paler colour. The latter pecu- 
liarity is due to their having fewer and paler chloroplasts. As soon 
as they are exposed to the light by the liberation of the overlying eggs, 
the chloroplasts begin to multiply and acquire a deeper colour, but the 
scars of two or three of the most recent crops can be easily distinguished 
from each other by their different shades of colour. 
II. The Development of the Antheridium. 
If a fresh plant of Dictyota be examined one to five days before the 
lowest neap tide the rudiments of the antheridia may be distinguished by 
their slight increase in diameter and their deeper colour, but chiefly by the 
pale circular area in the centre, indicating the position of the nucleus. 
Material fixed about this period would show the various stages in the stalk- 
cell mitosis, and perhaps also in the first division of the mother-cell of the 
antheridium. 
The antheridia, like the oogonia, are arranged in sori, but they are 
much more numerous than the former, the number in a fair-sized sorus 
being from one to two hundred. Each sorus has always a well-defined 
border of sterile cells consisting of three or more rows, the innermost of 
which are of about the same length as the antheridium, while the others 
successively diminish in height (Figs. 12-14). Some time after the libera- 
tion of the antherozoids the innermost border-cell cuts off a cell near the 
