136 Murphy .— The Morphology and Cytology of the 
age. The withdrawal is evidently not so rapid as the formation, several 
instances having been found. This again is contrary to the usual experience, 
as most authors state, if they mention it at all, that its further fate cannot 
be ascertained. There is some evidence to show that the wall is not 
perfectly elastic, so that when the difference in pressure is equalized it does 
not quite return to its original size or form. Thus one finds slight 
protuberances still jutting into the antheridium (Fig. 26). Even before this 
there is evidence of a gradual withdrawal to be found in a very deeply 
stained mass of cytoplasm lying in the oogonium at the mouth of the 
manocyst while the latter is still at or near its maximum size. * Whether 
it is entirely withdrawn by contraction, or whether the latter part of the 
process is one of eversion, is a very fine point and one not easy of solution. 
Cases which have been seen make it likely that both may occur, depend¬ 
ing on the extent to which the w r all was stretched, for the size of the 
body varies somewhat. The further discussion will be taken up under 
fertilization. 
The Oosphere and Fertilization. 
The nucleus which lies near the centre of the oogonium divides at 
about the same time as all the other nuclei. It is not later as a rule, as 
found by Kruger ( 22 ) in Albugo candida\ but small and irregular variations 
found by that author have been noted here too. The two daughter nuclei 
after division appear at first of about equal size (Fig. 20). They are 
considerably smaller than the parent nucleus and they stain very much 
less deeply. Good differentiation is not frequent. Soon afterwards, one 
of them begins to move away from the centre and at the same time to 
show signs of degeneration. Its further history is difficult to follow. 
Sometimes a degenerating nucleus is found at this stage some distance 
within the margin, but rarely, and it may well be a daughter nucleus from 
the centre. On the other hand, it may equally well be the daughter of 
a peripheral nucleus lying a little farther in than usual. It seems probable, 
however, that the removal from the future oosphere is effected by a wander¬ 
ing out and a dissolution which go on concurrently. However it is 
accomplished, there is but one functional female nucleus left in the oosphere. 
It still continues small and stains very faintly, and it often lies in a small 
irregular mass of slightly thicker cytoplasm which may represent the 
‘ central plasm \ This, however, cannot always be made out. The remain¬ 
ing contents of the oogonium require very careful study to make clear 
what is happening. 
The cytoplasm (Figs. 22 and 23) has reached its maximum attenua¬ 
tion, particularly in the centre. The central nucleus is so small and 
poor in chromatin that it may even be overlooked unless well stained. 
Its sister has disappeared, usually without leaving any trace behind it. 
