194 Lloyd Williams. — Studies in the Dictyotaceae. 
of the egg-nucleus is almost certainly an antherozoid. When compared 
with those that are lying outside the membrane it is seen to have greatly 
increased in size and to be somewhat fibrillar in texture. The egg-nucleus 
is in a prophase stage, but its appearance is more like that of partheno- 
genesis than of normal segmentation (see Figs. 22, 23). For some reason 
or other this particular spermatozoid, although it has entered the egg, 
has failed to reach the nucleus. Fig. 29 is still more curious. Here I 
regard the egg-nucleus, the one to the right, as having divided partheno- 
genetically, while the left-hand nucleus is probably an antherozoid nucleus 
which has failed to fuse with the former, but, at the expense of the egg 
cytoplasm, has greatly increased in size. On this view this is a stage 
further than the preceding one. 
IV. The Segmentation of the Fertilized Egg. 
The first reliable evidence of fertilization having been accomplished 
is the presence in the egg-nucleus of a second nucleolus, which is nearly 
always smaller than the original one (Figs. 21, 22, 23) ; this undoubtedly 
represents the chromatin brought in by the spermatozoid. Very soon 
the nucleoli present an appearance suggestive of their containing a number 
of deeply stained granules or chromosome-like masses. At the same time 
the chromatin thread is very fine and distributed through the whole of 
the nuclear space. After this the chromosomes are seen as thick curved 
rods, coarsely and irregularly beaded (Fig. 22). These after a slight increase 
in size are longitudinally split, and the chromatin disks become more 
distinct. The crowded appearance of the chromosomes at once suggests 
that they are more numerous than in the preceding stages : when they 
are counted the number in each case is found to be thirty-two. The 
nucleoli at this period are very irregular in form, but though they seem as 
if going to fragment they keep their coherence till the spindle stage. 
Returning now to a consideration of the extra-nuclear structures we 
find that in the unfertilized newly liberated egg, there is a zone of ‘ kino- 
plasm ’ surrounding the egg, and that outside this the chloroplasts tend 
to place their axes radially. At this period it is most difficult to find 
any recognizable centrosomes. In the stage represented by Fig. 21 
there is a centrosome and radiations on one side of the nucleus ; everywhere 
else the chloroplasts seem to be disposed without definite order, and in 
many instances they abut directly on the nuclear membrane. It is difficult 
to be quite certain about the number of centrospheres, but from all I have 
hitherto seen I am strongly inclined to think that there is only one. 
Fig. 24 shows an appearance which is so common as to lead me 
to think that it represents the normal mode of development of the seg- 
