;8 4 



EMBRYOLOGY 



motion in the Fallopian tubes 

 when sexual intercourse is fre- 

 quent (Williams). 



The head of the spermato- 

 zoid is about -5-^00" of an inch 

 (5 ft) long, g- oVo of an inch (3 /*) 

 broad, and ^^-Joo" ^ an ^ nc ^ 

 (i /x) in thickness. The tail 

 (flagellum) is about -5^ of an 

 inch (50 /-t) in length. The 

 length of the intermediate seg- 

 ment is about ^oVo f an i nc ^ 

 (6 /A). At the lower end of the 

 tail, is a short and excessively 

 Fig. ?.v$.spermatozoids, spermatic crystals and leu- fine filament, called the terminal 

 cocytes (Peyer). filament. The head contains a 



considerable quantity of chromatin. In the intermediate segment is 

 the centrosome. These play an important part in the process of fertili- 

 zation of the ovum. 



Water soon arrests the movements of the sperma- 

 tozoids, which may be restored by the addition of 

 dense saline and other solutions. All the alkaline 

 animal liquids of moderate viscidity favor the move- 

 ments, while the action of acid or of very dilute solu- 

 tions is unfavorable. The movements are suspended 

 by extreme cold, but they return when the ordinary 

 temperature is restored. 



Before puberty the seminiferous tubes are much 

 smaller than in the adult, and they contain small 

 transparent cells, which in their form and arrange- 

 ment resemble epithelium. As puberty approaches, 

 however, the tubes become larger, and the contents 

 change their character. 



In the adult testicle, the seminiferous tubes are 

 lined with two kinds of cells: I. The sustentacular 

 cells of Sertoli, and 2, cells situated between the 

 sustentacular cells, called spermatogonia. The sper- 

 matogonia, as they undergo development, become Left figure represents 

 attached to the sustentacular cells and probably are a side view; middle 



. . . figure, flat view; a, head; 



nourished by them. The spermatogonia multiply by b, centrosome; c, the 

 karyokinesis, with intervals of rest, during which the 

 quantity of chromatin increases. The daughter-cells, ment. 



pig. 214. Human 



