BIOLOGY OF SPERMATOZOA 



739 



tained varies considerably among species, 

 dependent as they are upon the estimates of 

 the time of fertilization. Reliable figures may 

 l)e expected in such forms as the guinea pig, 

 which is known to ovulate some 10 hours 

 after the onset of heat, or the rabbit which 

 ovulates about 10 hours after copulation. 

 But in women the exact time of ovulation 

 cannot be determined with sufficient accu- 

 racy to permit a precise statement as to the 

 duration of fertilizing capacity of the sper- 

 matozoa. The relatively long survival time 

 reported for the mare may reflect a kind of 

 thermal adaptation of the spermatozoa, be- 

 cause in the stallion the testicles are carried 

 in shallow scrotal sacs, the temperature of 

 which is probably close to that of the body. 



Hil)ernating mammals which copulate in 

 the autumn often show excessively long pe- 

 I'iods of sperm survival in the female (Hart- 

 man, 1933). In bats of the genera Myotis 

 and Eptcsicus, the spermatozoa inseminated 

 in the fall are capable of motility and of fer- 

 tilization at the time of ovulation in the 

 spring (Wimsatt, 1942, 1944), even though 

 subseciuent copulations may occur in nature 

 during the spring mating season (Pearson, 

 Koford and Pearson, 1952). Long-range 

 sperm survival is, of course, well known in 

 various poikilothermic animals, including 

 arthropods and lower chordates (see Hart- 

 man, 1939). Custodians of reptiles, particu- 

 larly, have recorded interesting breeding 

 data relevant to the longevity of sperm in 

 the female. Fertile eggs have been laid by 

 the diamond-back terrapin and various 

 snakes, 4 to 5 years after isolation; due to 

 the unlikelihood of delayed development, 

 this indicates sperm survival for periods of 

 several years (Barney, 1922; Haines, 1940; 

 Carson, 1945). 



Some attention has been directed toward 

 the possible deleterious effect of the aging 

 of sperm in the female tract ; although still 

 capable of fertilization, they might give rise 

 to abnormal or nonviable embryos (Austin 

 and Bishop, 1957). This change with senes- 

 cence has been well established in fowl 

 (Crew, 1926; Nalbandov and Card, 1943; 

 Van Drimmelen and Oettle, 1949; Dhar- 

 marajan, 1950), and might be expected to 

 occur in mammals; the evidence, however, 

 does not support it. Young's early data 



( 1931 ) indicated that guinea pig sperm, aged 

 in the male tract, could lead to an increase 

 in the percentage of abnormal embryos ; but 

 no such "overaging" effect was demonstrated 

 in sperm maintained in the female tract 

 (Soderwall and Young, 1940; Soderwall and 

 Blandau, 1941). 



Somewhat more recently, another type of 

 sperm behavior was discovered which in- 

 volves the capacity for fertilization (Austin, 

 1951; Chang, 1951b). This concerns not the 

 maximal limit of survival, but rather the ini- 

 tial attainment of full fertilizing compe- 

 tency, a continuation, in a sense, of the proc- 

 ess of sperm maturation long since begun in 

 the male genital tract. This phenomenon of 

 "capacitation," demonstrated thus far only 

 in rats and rabbits, requires 2 to 6 hours of 

 conditioning of the male gametes and prob- 

 ably involves both physiologic and struc- 

 tural alterations in the cells which enable 

 them to penetrate the zonae pellucidae of 

 the eggs (Austin, 1952; Austin and Braden, 

 1954; Chang, 1955, 1959). Capacitation is 

 assumed to occur normally in the female 

 genital tract. Under experimental conditions, 

 the injection of rat sperm into the periovar- 

 ian sac (Austin), or the introduction of rab- 

 bit sperm into the Falloi)ian tube (Chang), 

 accomplishes fertilization only after a de- 

 lay of several hours, unless the sperm have 

 been previously capacitated in another suit- 

 able reproductive environment. Such a mi- 

 lieu for rabbit sperm is afforded by the re- 

 productive ducts of female rabbits under a 

 variety of hormonal conditions, and by the 

 reproductive tracts of both immature ani- 

 mals and castrates, with or without the addi- 

 tion of gonadotrophin or estrogen (Chang, 

 1958). The uteri of pseudopregnant rabbits, 

 however, and those treated with progester- 

 one, were found unsuitable for sperm capaci- 

 tation. Some doubt has been cast upon the 

 s]iecificity of the factors which bring about 

 sperm conditioning by the demonstration, in 

 the rabbit, that not only does capacitation 

 occur in the uterus and Fallopian tube, but 

 also in such unusual environments as the 

 isolated bladder and colon of either male or 

 female animals and in the anterior chamber 

 of the eye as well (Noyes, Walton and 

 Adams, 1958a, b; Noyes, 1959b). 



As to the nature of the changes induced in 



