^6 ZOOLOGY. 



69. Reproductive Epithelium. The sexual cells, both male and female, 

 are developed from epithelium, -ectodermal, entodermal, or, as is usually 

 the case, mesodermal. The budding of the sexual epithelium, in the devel- 

 opment of the germ cells suggests the formation of glands (Figs. 18, 19). 

 The sexual cells often develop at the expense of the epithelial cells about 



them. 



FIG. 19. 



o 



FIG. 19. Section through ovary of a young Mammal (modified from Wieder- 

 sheim). The eggs (o) are seen to be formed from the epithelium by a process some- 

 what more complex than in Fig. 18. c, connective tissue of ovary; e, epithelium; f, 

 follicle of epithelial cells in which the ova ripen; o, ova in different stages of 

 ripeness. 



Questions on the figure. In the ovary of the mammal what addi- 

 tional service does the epithelial layer render the ovum after its forma- 

 tion? Is it apparent that there is anything gained by the sinking of the 

 ovarian follicles into the tissue of the ovary, instead of escaping imme- 

 diately, as in Fig. 18? 



70. Supportive or Connective Tissues. This class of 

 tissues embraces the bulk of the non-active tissues in animals. 

 They vary much in appearance and structure, agreeing in little 

 except in their mesodermic origin, their passivity, and in the 

 prevalence of intercellular substance. The intercellular sub- 

 stance gives the distinctive character to the connective 

 tissues, the cells having a relatively unimportant place 

 after the production of the intercellular substance. The 

 general function of the supportive tissues is to bind and 

 sustain the more active tissues in their relations to the 

 body as a whole. The classification of supportive tissues 



