

80 PRELIMINARIES TO FERTILIZATION 



tionate contribution made by the seminal plasma to this environ- 

 ment varies widely in different species. The environment afforded 

 by the female tract is presumably ideal for the preparation of the 

 spermatozoa for the task of reaching and entering the eggs. This 

 implies in most animals the existence of conditions favoring vig- 

 orous activity. The female environment is not necessarily the best 

 for the survival of the spermatozoa, and it is well known that the 

 life of the spermatozoon is much shorter in the female tract than 

 in the male (see Hartman, 1939). It would indeed be of little 

 advantage for the spermatozoa long to outlive the eggs. Never- 

 theless, the circumstances may occasionally favor longevity. Rel- 

 atively favorable conditions may exist in the cervical canal, and 

 it has been suggested that this region may act as a reservoir of 

 spermatozoa from which they are steadily released into the uterus 

 (Quinlan, Mare, and Roux, 1932, 1933; Starke, 1949), a situation 

 somewhat analogous to that of the "sperm nests" found in the 

 uterus of the domestic fowl ( Van Drimmelen, 1949, 1951 ) . How- 

 ever, the most remarkable instances of spermatozoon survival are 

 to be found among the bats, wherein the spermatozoa may retain 

 their fertility in the female tract for as long as five months (Re- 

 denz, 1929; Wimsatt, 1942, 1944). During this period they remain 

 embedded in high concentrations in the thick uterine mucus, 

 motionless but capable of exhibiting active motility upon dilu- 

 tion. Clearly, conditions within the bat uterus are highly special- 

 ized, for not only is the capacity of the spermatozoa for motility 

 retained but also the capacity for fertilization and for initiating 

 the development of normal individuals. Spermatozoa in the geni- 

 tal tracts of most other mammals soon enter a state of senescence 

 when these capacities are lost. The losses occur at different times 

 — the ability to form a viable embryo is lost before the ability to 

 fertilize eggs, and fertilizing capacity is lost before motility ( Van 

 Drimmelen and Oettle, 1949). In the fowl malformed, nonviable 

 embryos resulted when the eggs were fertilized with aged sper- 

 matozoa (Crew, 1926; Nalbandov and Card, 1943; Dharmarajan, 

 1950). There is evidence of similar changes in mammalian sper- 

 matozoa. Young (1931) found that the incidence of nonviable 

 embryos in the guinea pig could be increased from 3.6 to 20 per 



