178 EMBRYOLOGY. 



Describe the vagina. 



It is a membranous canal about 5 in. long, extending from the 

 uterus to the external genitals. It is lined with mucous mem- 

 brane, which in the ordinary contracted state is thrown into folds, 

 its anterior and posterior walls being in contact. There is consider- 

 able erectile tissue in the mucous membrane. At the orifice of the 

 vagina externally is a sphincter which only partially contracts it, 

 and besides this there are longitudinal and transverse unstriped 

 muscle-fibres in the submucous tissue. The outlet of the vagina 

 is sometimes also partially closed in the virgin by the hymen, a 

 fold of mucous membrane. 



What are the external organs of generation ? 



The external organs of generation are not immediately connected 

 with the function of reproduction, and may be enumerated as the 

 labia majora and minora, clitoris, and the meatus urinarius. 



What are the organs of generation in the male ? 



The two testicles which produce the seminal fluid, and the vas 

 deferens, or duct leading from each to the seminal vesicles, where 

 the secretion is stored until it is discharged through the penis. 



What is the structure of the testicles ? 



Each testicle is made up of a dense connective-tissue framework 

 and a secreting portion. The connective-tissue stroma, tunica albu- 

 ginea, surrounds the outside of the organ, and sends incomplete 

 partitions into the central portion of the organ, dividing it into a 

 number of communicating cavities. In these cavities are winding 

 tubules which constitute the secreting portion of the organ. These 

 tubules inosculate in a sort of mesh (reti test-is), and finally all 

 unite in the epididymis. The secreting tubules are called the 

 seminiferous tubules. 



How do the seminiferous tubules secrete the spermatic fluid ? 



Fach tubule has, in the active organ, a limiting membrane, upon 

 which are a number of layers of flattened cells. Internal to these 

 are seminal cells in two or more layers. The seminal cells contain 

 nuclei which are capable of division, so that each nucleus may de- 

 velop several new nuclei. The nuclei are the spermatoblasts. or cells 

 from which the spermatzoa originate. The cells before the division 

 of the nuclei resemble the ordinary cuboid epithelium, and it is in 

 the superficial layers (i. e. toward the lumen of the tubuli) that 

 this function of the cells takes place. 



