BIOLOGY OF SPERMATOZOA 



713 



testis from the epididymis of the guinea pig 

 increases transport time by 1 to 2 weeks, 

 possibly as a result of interruption of flow 

 of fluid through the excurrent ducts, or 

 perhaps as a consequence of operational 

 disturbances which involve changes in the 

 local vascularization and nerve supply. 



The vas deferens serves mainly for the 

 accumulation and storage of sperm, but 

 what sperm migration does occur seems pri- 

 marily dependent upon the muscular ac- 

 tivity of the duct. The vasa of the rat and 

 dog are normally quiescent in sexually in- 

 active males, but are capable under experi- 

 mental conditions, in vitro, of a high degree 

 of muscular activity (Martins and do Valle, 

 1938; Valle and Porto, 1947). Belonosch- 

 kin (1942) claimed that peristaltic activity 

 of the vas deferens aids in sperm transport 

 in man. 



B. SPERM SURVIVAL 



Spermatozoa may reside in the genital 

 tract for considerable periods of time before 

 being discharged at ejaculation. They gen- 

 erally lose their capacity for fertilization 

 before their capacity for motility during 

 storage in the ducts. Survival times vary 

 from several weeks to many months in dif- 

 ferent species. Bats normally store sperma- 

 tozoa over the winter months, and this may 

 be typical of certain other hibernating 

 mammals as well. Knaus (1933) claimed 

 that epididymal spermatozoa remain viable 

 and fertile for a year in vasectomized rab- 

 l)its, but the process of sperm renewal was 

 not eliminated in his experiments. Mouse 

 spermatozoa in the excurrent ducts main- 

 tain their capacity for fertilization for 10 

 to 14 days after spermatogenesis has been 

 inhibited by x-ray irradiation (Snell, 1933). 

 Rat epididymal spermatozoa, in animals 

 with ligated vasa, remain capable of mo- 

 tility for about 6 weeks, but lose their abil- 

 ity to fertilize eggs within 3 weeks (White, 

 1933b); castration further reduces sperm 

 survival to approximately 2 weeks (Moore, 

 1928). Likewise, in the guinea pig, after 

 ligation of the efferent ducts, epididymal 

 spermatozoa retain their capacity for mo- 

 tility some 60 days and for fertility 20 to 35 

 days; castration reduces motility to about 



3 weeks (Moore, 1928; Young, 1929b). 

 Translocation of the epididymis to the ab- 

 dominal cavity further limits sperm sur- 

 vival to about 2 weeks. When the rabbit 

 epididymis is anchored in the abdomen, 

 sperm motility and fertility are reduced 

 from about 60 and 38 days in the controls 

 to 14 and 8 days, respectively. Demonstra- 

 tions such as these seem to indicate that 

 body temperature may have a pronounced 

 effect even on relatively mature spermato- 

 zoa (Knaus, 1958) ; however, the transloca- 

 tion procedure may primarily affect the epi- 

 didymis, which in turn alters the longevity 

 of the spermatozoa. In at least one type of 

 natural experiment we have evidence that 

 excessive body temperature is seasonally 

 avoided by the gametes. In certain passerine 

 birds during the active breeding season a 

 transient thermal adaptation provides lower 

 temperatures for the storage of morphologi- 

 cally mature spermatozoa (Wolfson, 1954). 

 The sperm-engorged, distal ends of the vasa 

 deferentia here increase prominently in size 

 and become tortuously coiled, so as to re- 

 sult in a cloacal, scrotum-like swelling, the 

 internal temperature of which is about 4°C. 

 less than body temperature. 



When the testes have been separated 

 from the epididymides and time allowed for 

 recovery, the potential sperm capacity of 

 the duct system can be determined. Young 

 (1929b) found that guinea pigs, prepared 

 in this manner, can copulate successfully 

 as many as 20 times over a 2-month period. 

 The relative storage facilities of the major 

 segments of the ducts can be determined by 

 actual sperm count. Chang (1945) diligently 

 counted the sperm in the vasa and epi- 

 didymides of several ram genital tracts and 

 found the greatest accumulation in the tail 

 of the epididymis (Table 13.1). By frequent 

 ejaculation of the ram, approximately twice 

 a day, he further was able to estimate the 

 average rate of sperm production to be 

 about 4.4 X 10^ cells per day. In the bull 

 the rate is less, about 2.0 X 10^ sperm daily 

 (Boyd and VanDemark, 1957) ; most of the 

 epididymal sperm storage here is also in the 

 tail (45 per cent) compared with that in the 

 head (36 per cent) (Bialy and Smith, 1958). 



