XX IKTROLUCTION. 



tication, insalivation, deglutition, digestion, ab- 

 sorption, circulation, respiration, exhalation, ex- 

 cretion, secretion, and nutrition proper. It may 

 further be noticed that these functions, being from 

 their very nature necessary to the maintenance of 

 the organism, are performed throughout the entire 

 period of its existence. 



It is not so with the Functions of Reproduction, 

 the demand for which is often not manifested 

 until the life of the individual has approached 

 maturity, and even after that period it is not con- 

 stant, but occasional. Moreover, the discharge of 

 these functions, so far from being favom-able to 

 the maintenance of the organism, is, on the con- 

 trary, rather opposed to it, and it has even been 

 observed that in some animals death always occurs 

 shortly after the performance of the generative 

 function. 



The true generative act consists in the produc- 

 tion of germs, and their subsequent contact with 

 other bodies, termed * spermatozoa.' The young 

 germ is usually surrounded by a mass of nutrient 

 matter (or yolk), and the whole together consti- 

 tutes an *ovum.' The contact of the ova and 

 spermatozoa is termed 'fecundation.' Ova and 

 spermatozoa may be generated in the same or in 

 different individuals. Hence arises the distinction 

 of sex ; the power of producing ova being peculiar 

 to the female, while the formation of spermatozoa 

 devolves upon the male. It is well known that 



