258 GENERATION. 



tion iii the lower animals, except to illustrate the history of 

 development in man. 



The study of human generation will naturally assume the 

 following course : First, the female organs of generation, and 

 the formation of the female element, the ovum ; second, the 

 discharge of the ovum and the phenomena which attend this 

 process; third, the male organs, and the development and 

 discharge of the male elements, spermatozoids ; fourth, the 

 union of the two elements of generation, or fecundation; 

 fifth, the development of the fecundated ovum into the 

 foetus at term; sixth, the development of the body after 

 birth and at different ages, or stages of existence ; finally, 

 the natural cessation of the so-called vital functions, or physi- 

 ological death. . 



Sexual Generation. 



Before we describe the actual phenomena of sexual gen- 

 eration, as they are observed in man and the mammalia, it 

 will be interesting to note some of the salient points in the 

 history of our knowledge of this process in the inferior ani- 

 mals. This we can do, without exceeding the limits we have 

 laid dow^n in our general remarks. 



In the history of sexual generation, there seems to have 

 been a limiting line between the production of animals from 

 preexisting organisms and of those produced in some un- 

 known manner, or, as it has been said, spontaneously. This 

 line of distinction has always receded toward organisms lower 

 and lower in the scale of being with our advance in positive 

 knowledge. The ancients understood that the higher ani- 

 mals required for their production a concourse of the sexes ; 

 but they thought that many fishes, reptiles, insects, worms, 

 etc., were produced spontaneously. Indeed, with the limited 

 knowledge of natural history possessed by Aristotle and those 

 who succeeded him for many hundred years, the classes of 

 animals said to be produced spontaneously represented sim- 

 ,ply those, the generation of which was not understood. But, 

 as the habits of many animals became better understood, 



