CHAPTER TENTH. 



EMBRYOLOGY. 

 SECTION I. 



OF THE EGG. 



271. THE functions of vegetative life, of which we have 

 treated in the preceding chapters, namely, digestion, circu- 

 lation, respiration, and secretion, have for their end the pres- 

 ervation of the individual. We have now to treat of the 

 functions that serve for the perpetuation of the species, 

 namely those of reproduction, (200.) 



272. It has been generally admitted that animals as well 

 as plants are the offspring of individuals of the same kind ; 

 and vice versa, that none of them can give birth to individ- 

 uals differing from themselves ; but recent investigations 

 have modified to a considerable extent this view, as we shall 

 see hereafter. 



273. Reproduction in animals is almost universally accom- 

 plished by the association of individuals of two kinds, males 

 and females, living commonly in pairs or in flocks, each of 

 them characterized by peculiarities of structure and external 

 appearance. As this distinction prevails throughout the ani- 

 mal kingdom, it is always necessary, if we would obtain a 

 correct and complete idea of a species, to take into account 

 the peculiarities of both sexes. Every one is familiar with the 

 differences between the cock and the hen, the lion and the 

 lioness, &c. Less prominent peculiarities are observed in 



