SEXUAL REPRODUCTION. 1 95 



separation from the parental individual develops into a 

 many-celled body, and in this repeats the forms and vital 

 phenomena of the original producing organism. This last 

 form of monogonic propagation — that of the germ cells, or 

 spore-formation — leads us directly to a form of propagation 

 which is the most difficult of all to explain, namely, sexual 

 propagation. 



Sexual or aTnpJiigonic jpropagation (Amphigonia) is the 

 usual method of propagation among all higher animals and 

 plants. It is evident that it has only developed, at a very 

 late period of the earth's history, from non-sexual propaga- 

 tion, and apparently in the first instance from the method 

 of propapation by germ-cells. In the earliest periods of the 

 organic history of the earth, all organisms propagated them- 

 selves in a non-sexual manner, as numerous lower orofanisms 

 still do, especially all those which are at the lowest stage of 

 organization, and which, strictly speaking, can be considered 

 neither as animals nor as plants, and which therefore, as 

 primary creatures, or Protista, are best excluded from both 

 the animal and vegetable kingdoms. In the case of the 

 higher animals and plants, the increase of individuals, as a 

 rule, is at present brought about in the majority of cases by 

 sexual propagation. 



In aU the chief forms of non-sexual propagation mentioned 

 above — in fission, in the formation of buds, germ buds, and 

 germ cells — the separated cell or group of cells was able by 

 itself to develop into a new individual, but in the case of 

 sexual propagation the cell must first be fructified by 

 another generative substance. The fructifying male sperm 

 must first mix with the female germ-cell (the egg) before 

 the latter can develop into a new individual. These two 



