DEVELOPMENT OF THE SPERMATOZOA. 649 



as is seen in cases of extra-uterine foetation, when the ovum 

 develops in some unusual situation, such as in the Fallopian tube, 

 or in the abdominal cavity. 



The spermatozoa are formed by the cells lining the tubuli semi- 

 niferi of the testicle. These cells are cubical masses of proto- 

 plasm, which undergo rapid proliferation. The nuclei divide, 

 and from each part resulting from this division arises the head of 

 a spermatozoon, and the body is developed from the protoplasm 

 of the cell. The spermatic elements escape into the tubes, and 



FIG. 246. 



Section of the tubuli seminiferi of a rat. (Schafer.) a, Tubuli in which the sperma- 

 tozoa are not fully developed. 6, Spermatozoa more developed, c, Spermatozoa fully 

 developed. 



pass down the vasa deferentia into the vesiculaB seminales, where 

 they either undergo a retrograde change or are cast out of the 

 body. 



The ovum arises from the differentiation of one of the cells of 

 the germ epithelium covering the surface of the ovary. A group 

 of these cells, entering the periphery of the ovary, becomes there 

 imbedded in a kind of capsule derived from the surrounding 

 areolar tissue of the stroma, and forms an immature Graafian 

 follicle. One of the cells grows rapidly to become the ovum, the 

 55 



