Trow . — On Fertilization in the Saprolegnieae. 561 
Strasburger (’01) has expressed himself very strongly as to the improbability 
of their presence in the higher plants. It may be regarded as doubtful 
whether the blepharoplasts described by Belajeff (’98 and ’99), Shaw (’98), 
Webber, Ikeno, and Hirase in various Vascular Cryptogams and Gymno- 
sperms are the homologues of the centrosomes found in Thallophytes and 
liverworts. In any case a critical summary of the present state of our 
knowledge as to the occurrence and distribution of centrosomes in plants 
appears to be a desideratum. In the genera mentioned above the male 
gametes have been critically examined in Fuats alone, and fortunately by 
such expert cytologists as Strasburger, Farmer, and Williams. Strasburger, 
in particular, paid special attention to the possibility of the existence of 
a male centrosome and astrosphere, being fully alive to the significance of 
its presence or absence in view of the current theories of fertilization. The 
observations of Farmer and Williams (’96, ’98) are of special interest. 
They state ‘ the passage [of the antherozoid] through the cytoplasm [of the 
oosphere] is extremely rapid, as is proved by the rarity of specimens which 
we have obtained which show the antherozoid between the egg periphery 
and the centrally placed nucleus. In its path through the cytoplasm it 
rather resembles a chromatophore, from which, however, its reaction to 
stain readily serve to distinguish it. It travels towards its destination 
with its blunter end forward , and no trace of cilia could be discerned when 
it was once inside the egg.’ An examination of the excellent figures of 
these three observers leaves little doubt that the sperm -nucleus in Fucus is 
destitute of a centrosome and astrosphere. 
Male centrosomes and astrospheres are well known in animal eggs, 
and are especially well developed apparently in Echinoderms. It is 
interesting to note that that rotation of the axis of the sperm-nucleus and 
consequent change in position of the astrosphere which has been so often 
described, and is very beautifully illustrated for Toxopneustes by Wilson 
(’97), does not take place in Achlya. During the progress of the sperm- 
nucleus to the middle of the oosphere it appears to keep its astral rays 
directed constantly towards the periphery. This behaviour corresponds to 
that described as occurring in Fucus by Farmer and Williams, making the 
necessary allowance for the absence of the astrosphere in the Alga. The 
male astrosphere certainly influences the female, for that appears to be 
repelled and to be driven thus from its central position in the oospore 
(Figs. 28 and 29 ). When the sperm-nucleus reaches the central region of 
the oospore, the dense protoplasm accompanying it goes to swell the 
ovocentrum, and this regains its original central position (Fig. 28 ). The 
ovocentrum now encloses two nuclei, two centrosomes, and two astro- 
spheres. 
Disappearance of the astrospheres and ovocentra and the fusion of the 
game to -nuclei. The detection of the male astrospheres proved difficult. 
