BIOLOGY OF SPERMATOZOA 



711 



including its relative fertilizing capacity. 

 The precise nature of the impairment is un- 

 known but seems to involve the ability of 

 the sperm to traverse the uterotubal junc- 

 tion (Braden and Gluecksohn-Waelsch, 

 1958). This is the same gene which Bryson 

 (1944) found to affect both sperm morphol- 

 ogy and motility in the heterozygous (^V^^) 

 male. These results are yet fragmentary but 

 are strongly indicative of the fact that 

 spermatozoa reflect their haploid genotype 

 and that when they bear an unfavorable al- 

 lelic constitution they may display a de- 

 creased fertilizing potential. The possibility 

 exists that subviable mutants, recessive in 

 the heterozygous condition, might have pro- 

 found detrimental effects when segregated 

 into particular gametes. 



C. REQUIREMENTS FOR LARGE 

 SPERM NUMBERS 



Any suggestion at the present time to 

 justify the large number, or ''excess," of 

 sperm ordinarily involved in insemination is 

 at best a hazardous supposition. The earlier 

 speculations which presupposed a sperm 

 ''swarm" to supply hyaluronidase for the 

 dissipation of cumulus cells (McClean and 

 Rowlands, 1942) are inconsonant with the 

 facts, since only a very few sperm, on the 

 order of 25 to 250, are to be found in the 

 presence of fertilized eggs of rats, rabbits, 

 and ferrets, for example, while the cumulus 

 cells are still clustered about the eggs (Bra- 

 den and Austin, 1953; Chang, 1959). That 

 many more sperm are produced and in- 

 seminated than are necessary for fertiliza- 

 tion is not be to denied. A phenomenon im- 

 plicating survival of the species can be 

 expected to have built-in safety factors, and 

 sperm production is no exception, particu- 

 larly if the male is to be capable of frequent 

 ejaculation. Very probably, the pattern for 

 high gametic production was set long ago 

 among animals which reproduced by means 

 of external fertilization where sperm, egg, 

 and larval loss are very high. In fact, ob- 

 stacles to successful fertilization are present 

 in mammals as well; definite blocks to 

 sperm transport, for example, occur at the 

 cervix, uterotubal junction, and tubal isth- 

 mus in many animals. But it is to be em- 

 phasized, in the light of evidence cited in 



the two preceding sections, that the waste 

 of healthy spermatozoa may be less than 

 previously conjectured. The exigencies of 

 the complex series of cellular and functional 

 changes which ensue during the passage of 

 sperm through the genital tracts and the 

 possibility of genetic variation with conse- 

 quent differences in fertilizing capacity sug- 

 gest that the number of physiologically ef- 

 fective sperm in the ejaculate may be but a 

 fraction of the total inseminated. 



III. Sperm Transport and Storage 

 in the Male Tract 



Aside from the accessory reproductive 

 glands that supply, in large measure, the 

 constituents of the seminal plasma (see 

 chapter by Price and Williams-Ashman), 

 the male genital tract of vertebrates is es- 

 sentially a collection and transport system, 

 designed to convey the spermatozoa from 

 the testis to the ejaculatory duct (Fig. 

 6.1). It does more than this, however, in 

 that the gametes, on the one hand, are 

 altered in their capacity for fertilization 

 and, on the other hand, are stored, motion- 

 less, often for long periods of time, prepara- 

 tory to ejaculation. The intrinsic changes 

 within the maturing sperm and the inter- 

 relations between the gametes and the vari- 

 ous segments of the male duct system are 

 only just beginning to be appreciated. The 

 cytologic integrity and the functional ac- 

 tivity of the male reproductive ducts are 

 directly influenced by the androgen output 

 of the testicular interstitium and presuma- 

 bly vary in their influence on the spermato- 

 zoa within the tract. Spermiation, the re- 

 lease and shedding of spermatozoa from 

 the testes of amphibians, is, of course, hor- 

 monally induced (Van Oordt, Van Oordt 

 and Van Dongen, 1959; Witschi and Chang, 

 1959) ; the mechanism of release is dis- 

 cussed elsewhere in this volume (chapter 

 by Greep) . In the cock, which has no glands 

 analogous to the seminal vesicles or pros- 

 tate, "seminal" fluids are contributed by the 

 seminiferous tubules and vasa efferentia 

 (Lake, 1957). 



A. SPERM TRANSPORT 



It can be stated with reasonable assur- 

 ance that sperm migration within the male 



