BIOLOGY OF SPERMATOZOA 



709 



terms, it represents a continuity, of part at 

 least, of the germ plasm from one generation 

 to the next. In a very real phylogenetic 

 sense, the gamete is one haploid generation 

 momentarily sandwiched between two ex- 

 tended diploid generations. 



Sperm, unlike most cells, are designed to 

 function outside of their native environ- 

 ment. Where fertilization is external, sper- 

 matozoa may be shed into an aqueous me- 

 dium of different ionic strength which offers 

 little shelter, scant buffering capacity, toxic 

 ions, and a lack of energy substrate essential 

 for extended metabolic activity. In the case 

 of internal fertilization, on the other hand, 

 these conditions are generally obviated, and 

 the seminal plasma, the vehicle for trans- 

 port, affords additional security features 

 beneficial to sperm survival. However, the 

 introduction of sperm into the female ani- 

 mal places them, even here, in foreign sur- 

 roundings which, although natural, may not 

 always prove hospitable. There is evidence 

 to indicate, for example, that the normal 

 protective and immune responses of the fe- 

 male against foreign invasion reach even to 

 the oviduct and uterus and to their luminal 

 secretions. 



The motility of typical spermatozoa is 

 certainly their most striking characteristic. 

 Indeed, the degree of motility is frequently 

 equated to fertilizing capacity and survival. 

 The sperm of many nonmammalian species, 

 however, may appear quite immotile, al- 

 though they are fully capable of fertilizing 

 normal eggs. The sperm of the herring {Clu- 

 pea) , for example, are immotile as shed and 

 remain so until brought into the vicinity of 

 homologous eggs (Yanagimachi, 1957). The 

 giant sperm of the hemipteran insect, Xoto- 

 necta glauca, show no movement until acti- 

 vated by fluids from the female genital sys- 

 tem (Pantel and de Sinety, 1906). The 

 sperm of many invertebrate animals, more- 

 over, are nonflagellated, a specialization 

 particularly common among decapod Crus- 

 tacea. Amoeboid spermatozoa are found 

 among ascarids, and in the sponge, Grantia, 

 it is claimed that the sperm lose their fla- 

 gella and are engulfed by modified collar 

 cells which transform into amoeboid forms 

 and transport the parasite-like sperm to the 

 oocytes (Gatenby, 1920). It thus appears 



that, whereas nature has endowed the male 

 gametes with fiagella from the lowest pro- 

 tistan to the highest mammal, she has de- 

 veloped secondary modifications toward less 

 specialized conditions among numerous or- 

 ganisms between the evolutionary extremes. 



II. Functional State of Gametes 

 after Spermatogenesis 



The gross structure and organization of 

 sjiermatozoa are generally considered com- 

 plete when the gametes leave the testis. The 

 statement is frequently seen that spermato- 

 zoa, as found in the male efferent ducts, are 

 ready for fertilization, unlike the egg cells 

 which often, and in all mammals, are ovu- 

 lated in a cytogenetically incomplete state 

 of development, later to be activated by the 

 sperm. In a general way, this contrast in the 

 functional activity of the gametes is real- 

 ized, and the most cogent evidence in behalf 

 of the fertilizing capacity (although less 

 than normal) of testicular sperm is the rec- 

 ord of conceptions resulting from insemina- 

 tion by sperm removed from the gonads of 

 chickens and men (Munro, 1938; Adler and 

 Makris, 1951). Normally, however, the 

 process of sperm maturescence is not com- 

 plete until some time after sperm formation, 

 and fertilizing capacity is fully realized 

 only after a period of sojourn in the male 

 and female genital tracts (Redenz, 1926; 

 Young, 1929a, 1931; Munro, 1938; Bishop, 

 1955). 



A. THE MATURATION OF SPERMATOZOA 



A number of structural and physical 

 changes, here only briefly noted, occur in 

 spermatozoa during transit through the 

 ducts. Morphologically, the most obvious 

 modification is the loss of the "kinoplasmic 

 droplet," a cytoplasmic residuum of dubious 

 function characteristic of immature cells 

 and only rarely found in sperm of a normal 

 ejaculate (Merton, 1939a; Gresson and 

 Zlotnik, 1945; Mukherjee and Bhattacha- 

 rya, 1949). Less obvious changes are a con- 

 comitant decrease in free-water content and 

 an increase in specific gravity of sperm as 

 they mature, as in the bull (Lindahl and 

 Kihlstrom, 1952). Salisbury (1956) found 

 evidence to indicate that changes occur in 

 permeability to water and in intracellular 



