THE GERM CELLS. 



Acrosome 



X~\ 



Galea 

 capitis 



Neck HHC Anterior end knob 

 Posterior end knob 



Body 



End ring 



Spiral fibers 



Sheath of 

 axial thread 



posterior end knob, is situated a little farther back. A derivative of the centro- 

 some, as shown during development of the spermatozoon, is the end ring 

 which marks the boundary between body and tail. 



Spermatozoa of other animals, both vertebrates and invertebrates, show a 

 great variety of forms. A few of these are 

 illustrated in Fig. 5. Some are simple in 

 form and structure, others are complex and 

 even bizarre. Almost throughout the 

 series, however, there is some structure Head* 

 that lends itself to the function of motility. 



In the tubules of the mammalian testis, 

 where the spermatogenic cells develop into 

 the mature spermatozoa, the sperms are 

 not motile. They acquire some degree of 

 motility in the tubules of the epididymis 

 and the highest degree only after they are 

 mixed with the secretions of the prostate 

 gland and other accessory sex glands. 

 They are active in the fluid of the female 

 genital tract where they swim against the 

 current produced by the cilia of the epithe- 

 lium -lining the tract. Their rate of 

 progress has been variously estimated from 

 1.5 to 3.5 mm. per minute. It is not 

 known how long spermatozoa remain alive 

 in the female genital tract. They have 

 been found in the vagina seventeen days 

 and in the cervix of the uterus eight days 

 after cohabitation, and in one case where 

 the oviducts were removed more than 

 three weeks after cohabitation active 

 sperm cells were found but whether they 

 were capable of fertilizing an ovum could 

 not be determined. Spermatozoa can en- 

 dure considerable variation in tempera- 

 ture; they are most active in a slightly 

 alkaline medium but die quickly in an acid 

 medium. The number of spermatozoa 

 produced by an individual is almost incomparably greater than the num- 

 ber of ova. It has been estimated that only about 400 ova reach maturity 

 during the reproductive period of a little more than 30 years in a 



Main segment 

 of tail 



Axial thread 

 -Capsule 



Terminal 

 filament 



FIG. 4. Diagram of a human 

 tozob'n. Meves, Bonnet. 



^ 



