GENERAL HISTOLOGY. 



79' 



gland-cells are usually scattered among ordinary epithelial cells, 

 so the sexual cells, almost without exception, lie embedded in 

 epithelium; it maybe in the epithelium of the skin (fig. 32), of the 



FIG. 32. Germinal epithelium of a medusa, eh, ectoderm; en, entoderm ; o, egg; 



e, epithelium. 



gut, of the body cavity, or of parts cut off from this (fig. 33). 

 This connexion of the sexual cells with the epithelium has a 

 deeper meaning in the fact that many organisms, and particularly 

 organisms of low structure, consist exclusively of epithelia and 



FIG. 33. Section through the ovary of a new-born child. (After Waldeyer.) ge T 

 germinal epithelium; pe, primitive egg in the germinal epithelium; p, egg-pouch; 

 g. egg-nest constricted off from the pouchlike growth (p); /, single egg with fol- 

 licle; r, blood-vessel. 



therefore must necessarily develop their sexual products in 

 epithelium. In other words, sexual and epithelial cells are the 

 oldest elements of the animal body, and hence very early came 

 into relation with one another. 



Sexual epithelium (or, as it is often called, germinal epithe- 

 lium) like glandular epithelium has a tendency to grow into the 

 subepithelial tissues in the form of isolated or branching tubes 



