REPRODUCTION 



the histona the first is called the egg-cell {ovulum), and 

 the latter the sperm-cell {spermium, or spermatozoon). 

 As a rule the latter is a very mobile ciliated cell, the 

 former an inert or amoeboid cell. The vibratory move- 

 ments of the sperm-cells serve for approaching the 

 ovulum in order to fertilize it. 



The qualitative difference between the two copulating 

 sexual cells {gonocyta), or the chemical difference be- 

 tween the ovoplasm of the female and the sperm-plasm 

 of the male cell, is the first (and often the only) condition 

 of amphigony; subsequently we find in addition (in the 

 higher histona) a very elaborate apparatus of secondary 

 structures. With this chemical difference is associated 

 a peculiar double form of sensitive perception and an 

 attraction based thereon, which is called sexual chemo- 

 taxis or erotic chemotropism. This "sex-sense" of the 

 two gonocyta, or elective affinity of the male androplasm 

 and the female gynoplasm, is the cause of mutual attrac- 

 tion and union. It is very probable that this sexual 

 sense-function, akin to smell or taste, and the movements 

 it stimulates, are located in the cytoplasm of the two sex- 

 cells, while heredity is the function of the caryoplasm of 

 the nucleus. {Cf. the Anihropogeny, chapters vi. and vii.) 



The sexual difference between the two forms of gono- 

 plasm, the ovoplasm of the female and spermoplasm of 

 the male cell, is noticeable at the very beginning of 

 sexual differentiation in the different sizes of the cop- 

 ulating gameta, and later in their increasing diver- 

 gence as to shape, composition, movement, etc. It leads 

 further to the distribution of the germmal regions (in 

 which the sex-cells are formed) into two different in- 

 dividuals. When the ovum and the sperm-cell are pro- 

 duced in one and the same individual, we call this an 

 hermaphrodite; and when they are formed in two dif- 

 ferent individuals (male and female), we call them 

 monosexual, or gonochorists. In accordance with the 



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