24 The Significance of Sex. [Jan. 
I.—Introduction. 
í 
HAT is the significance of sex ?” is a special inquiry in the 
more general field of research included under the head of 
Reproduction ; but nearly all the problems of the larger subject 
must be investigated if we wish to elucidate the more special 
one. The question presents both morphological and physiological 
aspects. Thus, we need to know the intimate structure of the 
sexual cells in the different plants and animals and the modi- 
fications this structure undergoes from the time the cells are 
generated until fertilization is effected. We can in this way 
compare the ovum and the spermatozoon and perhaps learn 
whether their functions are alike or different, and in what they 
differ. But we must also know how they compare with other 
cells, and are therefore at once compelled to treat the general 
subject of Cytology. This may conveniently be done in the fol- 
lowing order: (1) Cell-structure in general. (2) The structure 
of sexual cells; the ovum (practically the germinal vesicle) and 
the spermatozoon. (3) The phenomena of karyokinesis. (4) 
The phenomena of fertilization. 
Then in the next place it is necessary to make a comparative 
study of the methods of reproduction in the groups of living 
beings, following the phyla of evolution. In unicellular organ- 
isms we shall be mainly interested in the various ways in which 
reproduction is effected and the relation of these to the action 
of environing circumstances. Here we may see the origin of 
sex and henceforth trace its evolution. Then as we see how the 
multicellular individual arose from the unicellular one, and as 
- we trace the evolution of more and more complex forms, differ- 
entiating into more and more numerous groups, the relations of 
the sexual method to other methods of reproduction will gain in 
interest and be best considered under the heads of Alternation of 
Generations and of Parthenogenesis. We shall also be specially 
interested in following the genesis of the sexual cells during the 
life-history of each individual, and so be involved in the mazes 
of ovigenesis and A OESE Incidentally hermaphroditism 
should be and finally the morphological side of the 
-~ question must as wih a discussion of the —— 
_ the polar E and allied points. 
