88 FECUNDATION }; HETEROGAMETES. 
an unrecognizable condition. In the light of what is known in certain 
animal eggs such an inference was tempting, but, from our present 
knowledge of the centrosphere and centrosome in plants, such a con- 
clusion is no longer justifiable. Moreover, when the centrospheres 
appear in the first nuclear division of the fecundated egg, it is difficult, 
and may be impracticable, to distinguish between the male and female 
portions. 
Only in rare cases does more than one spermatozoid enter the egg, 
for among several thousand preparations examined by Farmer and 
Williams, only three cases of polyspermy were observed in which two 
spermatozoids had effected an entrance. The rare occurrence of poly- 
spermy under such conditions as are normal for the plants concerned, 
and as appears favorable for this phenomenon, would seem to indicate 
that many cases of polyspermy reported for animals might be largely 
the result of the prevalence of abnormal conditions at the time of 
fecundation. 
Concerning the large odsphere-like bodies with two nuclei in Fucus, 
which have been regarded by Behrens as fecundation stages, the joint 
authors cited above state with emphasis that these “ represent either 
abnormally developed odspheres or oogonia.” 
VOLVOX. 
Without implying any relationship whatever between the two groups 
of plants to which they belong, the sexual process in Volvox may be 
fittingly mentioned along with that of Aucws. In this most highly 
differentiated representative of the Volvocacee we have highly special- 
ized sexual cells, and in fact, as has been already stated in a preceding 
chapter, there is in this group of plants, as in the brown alge, a 
gradual transition from the simplest form of sexual reproduction of 
isogametes to that of the well differentiated bisexual elements of Volvox. 
Some authors (Strasburger, ’92, 1900; Overton, ’89) regard the 
spermatozoid of Volvow as a transition between the motile isogametes 
of alge and the spermatozoids of the Characeez, The spermatozoid 
of Volvox globator tapers gradually to a slender anterior end which is 
colorless, the thicker posterior end being yellowish. At the boundary 
between the two lies the red eye-spot, and a little farther forward are 
borne the two laterally inserted cilia. It is reasonable to assume that 
the cilia spring from a blepharoplast, although positive proof is still 
wanting. Strasburger (1900, p. 196) regards the colorless and slender 
anterior end as the homolog of the mouth-piece of algal gametes, from 
which such highly differentiated bisexual elements as those of Volvox 
