486 



THE REPRODUCTIVE SYSTEM 



spermatozoon. This is tipped with an aerosome, a derivative of the 

 idiozome, and covered by the galea capitis, the two comprising the per- 

 foratorium. The other constituents of the idiozome contribute the 



central filament. The extent between distal and 

 proximal centrosomes constitutes the neclc; the 

 portion between distal centrosome and ring cen- 

 trosome the connecting or middle piece (body), 

 with its spiral filament derived from mitochon- 

 dria. The tail or flagellum consists of central 

 filament enveloped by cytoplasm. In many forms 

 a spiral fin develops on the body. Also, there is 

 endless variation with reference to the shape of 

 the head. But the development and morphology 

 of spermatozoa of all vertebrate forms is essen- 

 tially the same. At fertilization only head and 

 middle piece nucleus and centrosome and mito- 

 chondria enter into the egg, the tail being gen- 

 erally left behind. 



The human spermatozoon has a length of from 

 fifty to sixty microns. Of the total the head con- 

 stitutes about 5 p., the middle piece about 5 /* and 

 the end-piece about 10 p.. Seen en face the head 

 has an ovoid shape ; in profile it appears pyriform, 

 due to a thinning along its terminal margin. Oc- 

 casionally atypical or monstrous, double-headed, 

 multiple-tailed, and giant spermatozoa appear ; but 

 these are probably non-functional. Though flagel- 

 late, the spermatozoa are non-motile until they 

 reach the epididymis, where they become bathed in 

 a secretion. Their motility, however, is not pro- 

 nounced until they reach the place in the excretory 

 passage where the secretion of the seminal vesicles, 

 prostate and bulbo-urethral glands are present. 

 The mixture of these secretions with the sperm 

 forms the semen. 



The spermatozoa can withstand considerable variations in tempera- 

 ture, but they are very susceptible to acid solutions ; they survive best 

 in slightly alkaline media. Under favorable conditions spermatozoa 

 may be kept alive for as long as eight days; it is probable that they 

 remain alive for even a longer time in the female genital tract; but 



Fia. 431. SPERMATO- 

 ZOA OF VARIOUS AN- 

 IMALS. 



A, from the badger; 

 B, from the bat. Re- 

 drawn after Ballowitz. 

 X 1200. C, from the 

 rat. Hematein and eo- 

 sin. X 1200. 



