UNION OF SPERMATOZOA WITH GERM-CELLS. 277 



molluscous animals the male and female organs exist in the 

 same individual, so that such individual impregnates itself; 

 which is, in fact, what happens in the major part of phanero- 

 gamous plants. In all vertebrate animals the male organs 

 exist in one individual, the female organs in another individual. 

 The germ-cells produced in the ovaries are discharged from 

 these organs at intervals (in the human female at the mens- 

 trual periods), and would be always thrown off from the 

 system without further development, did they not upon occa- 

 sion meet with vibratile particles formed in the male organs. 

 These vibratile particles are the spermatozoa. Thus, germ- 

 cells derived from the ovary, and spermatozoa or spermato- 

 zoids derived from the testes, are essential to reproduction. 

 For a long time it was the general persuasion that the mere 

 contact of the vibratile spermatozoid with the ovule was all 

 that is essential to impregnation ; but it is now proved by 

 abundance of evidence that the spermatozoid actually makes 

 its way through a minute aperture into the ovule, or that the 

 elements of male origin are actually blended with the elements 

 of female origin. It is supposed that this blending of elements 

 derived from each parent in the very outset of reproduction, 

 affords an explanation of the resemblances that exist between 

 parents and their offspring in feature as well as in bodily and 

 mental qualities. According to popular belief, the child, in 

 what relates to outward form, gait, and manners, takes after the 

 father, while it draws upon the mother in regard to size and in- 

 ternal qualities and dispositions. There can be no doubt that 

 any such rule is liable to large exceptions. As a general law, 

 however, it is said to hold very extensively among cattle. 

 " Such facts seem in their turn to be accounted for by the 

 circumstance that the spermatozoid enters and melts down in 

 the external parts of the yolk of the egg that is, in connec- 

 tion with those layers of the germinal membrane which form 



