THE EGG 



The lowest part of the genital canal, the vagina, is lined 

 with a membrane made of cells many layers thick (Plate 

 XIII, A)f closely resembling the structure of skin, except 

 that the latter is dry and somewhat scaly, while the vaginal 



Secretion. 



Fig. 13. Diagram representing a gland like those of the uterus, consist- 

 ing of a tube of cells dipping down from the surface. This is surrounded 

 by a network of capillary blood vessels, from which water and other 

 substances pass through the gland cells, undergoing chemical elaboration, 

 and are discharged into the central channel of the gland and thus reach 

 the cavity of the uterus. 



lining is moist. The lining of the vagina, in fact, becomes 

 continuous with the skin of the outside of the body, at the 

 vaginal orifice, just as the membranes of the nose, mouth, and 

 lower intestine become continuous with the skin. 



Fertilization and segmentation of the egg. Sperm cells 

 deposited in the vagina by the male make their way up 



{ 55 } 



