1887] The Significance of Sex. 221 
clei at the other end (s’) are the antipodal cells. In æ the male pronucleus has en- 
tered the ovum. In å the two have fused, but the nucleoli are still separate. In c the 
nucleoli are one; and in d the first segmentation spindle of the embryo is formed. 
fits 133. A segmentation spindle from the egg of Aulostomum gulo—Nussbaum, 
. m. A., xxvi.—To show the direct continuity of spindle-fibres with the yelk retic- 
aa 
(d) FERTILIZATION. 
aen fecundation, copulation, conjugation, zy- 
gosis, are Some of the terms used indiscriminately when 
referring to the fusion of sexual elements. We may refer to the 
Jusion of nuclei, or of cells; or simply to the apposition of cells, 
or of individuals for sexual purposes. We shall use the term con- 
Jugation always in the former sense and copulation always in the 
latter. Thus we shall use the term copulation where other writers 
say “temporary conjugation.” Conjugation of cells when not 
followed by conjugation of the nuclei produces plasmodia; we 
might u$e the term zygosis when fusion of the nuclei is involved. 
Polyspermy is where more than one male cell fuses with a female 
cell; and superfecundation implies, or should imply, the conjuga- 
tion of more than two nuclei to form one zygote. We need one 
term more, and that is where, in polyspermy, the female nucleus 
segments by stenosis to furnish a partner for each of the male 
nuclei. For this case we would suggest the term mu/tifecunda- 
tion. 
The modern theory of fertilization dates from the birth of the 
cell theory, when Kolliker extended its scope by advancing the 
view that the spermatozoon is a cell, and that it fertilizes the egg 
by a fusion with its substance, as against the theory that it was 
the fluid portion of the semen which holds the impregnating 
power. This view was not established until 1847, although 
Barry had seen the spermatozoon penetrate the ovum in 1843. 
It was now possible to compare fertilization with the conjugation 
which successive years of study continued to discover in the dif- 
-ferent groups of plants and animals, but with this line of devel- 
opment we are not here concerned. 
In 1827, Baer described as maturation of the ovum the changes 
which the egg nucleus suffers, and Purkinje three years later 
_ named this nucleus the germinal vesicle, because it bursts and lets 
out its “generating lymph” through the germ. Attention was 
first called to the polar globules by Dumortier, and Müller named 
them direction corpuscles in 1848, because he thought they fixed 
