BIOLOGY OF SPERMATOZOA 



723 



tlie entire field of i'e|)r()(liu'tive physiology 

 and animal breeding. 



A. EJACULATION 



The ejaculatory response in many mam- 

 mals occurs seasonally, corresponding to 

 periodic activity of the testes and accessory 

 glands, and is dependent on a variety of 

 neurohumoral factors. In some animals, in- 

 cluding man, potency continues throughout 

 the period of reproductive maturity. Vol- 

 ume of semen and s})erm concentration, be- 

 ing contingent on both secretory activity of 

 the accessory glands and spermatogenic ac- 

 tivity of the gonads, vary with successive 

 collections. Repetitive ejaculation can "ex- 

 haust" the sperm supply (Table 13.4), and 

 >uch procedures have been used, albeit with- 

 out great practical success, to test the sper- 

 matogenic productivity of man and of vari- 

 ous domestic animals. 



The potential for ejaculation of many 

 animals is quite striking. Carpenter (1942) 

 observed that free-ranging macaque mon- 

 keys are capable of ejaculating 4 times a 

 day for 3 or 4 days, whereas the so-called 

 "black ape" (a baboon, Cijnopithecus) , 

 studied by Bingham (1928), ejaculated 3 

 times in 20 minutes. Domestic cats have 

 been known to inseminate 10 females within 

 1 hour, and rabbits, 38 to 40 does in 8 hours 

 (Ford and Beach, 1951). White rats can 

 ejaculate 4 times in 15 minutes and as many 

 as 10 times during a 3-hour period. Chang 

 and SheafTer (1957) reported that a golden 

 hamster copulated 50 times in an hour, with 

 ejaculation occurring during most of the 

 mounts. ]\IcKenzie and Berliner (1937) col- 

 lected 20 ejaculates in 1 day from a ram, 

 the 19th sample of 0.66 ml. containing over 

 1 l>illion sperm, compared with the first 

 ejaculate of 0.7 ml. which contained 3.5 

 liillion cells. 



There is relatively little correlation be- 

 tween the number of intromittent thrusts 

 and the number of actual ejaculations, or 

 between the duration of copulation and the 

 volume of seminal discharge. In rodents, for 

 example, intromission may occur as many 

 as 80 to 100 times before ejaculation, or in- 

 semination may occur on the first intromis- 

 sion. Copulation in the macaque may in- 

 volve several dozen mountings and well over 

 a hundi-ed pelvic thrusts before ejaculation 



TABLE 13.4 



Chanyes in volume and sperm (lensitt/ of hull 



ejaculates collected frequently throughout a 



one-hour period 



(From T. Mann, Advances EnzvmoL, 9, 



329-390, 1949.) 



occurs. The prolonged copulation of the fer- 

 ret and sable, as long as 3 hours, represents, 

 not excessive ejaculation or insemination, 

 but rather a functional adaptation to de- 

 layed ovulation (Ford and Beach, 1951). In 

 the dog, however, the mounting time is 

 roughly proportional to the duration of 

 ejaculation, averaging in several breeds 

 about 6V2 minutes (Perez Garcia, 1957). An 

 important accomplishment of genital activ- 

 ity, at least in the rat, is the stimulation of 

 sufficient corpus luteal function to support 

 pregnancy (Ball, 1934). 



Cerebral and constitutional influences in- 

 cite and modify the physiologic processes of 

 both erection and ejaculation (Rommer, 

 1952) under the direct innervation by lum- 

 l)ar centers operating through muscular and 

 vascular mechanisms. Spinal section in man 

 does not necessarily prevent seminal emis- 

 sion (Ford and Beach, 1951). The relevant 

 neural pathways in man have been sum- 

 marized by Whitelaw and Smith wick (1951) 

 from their observations on partially sympa- 

 thectomized patients (Fig. 13.4, a and b) ; 

 sympathetic fibers and the second, thii'd, 

 and fourth sacral parasympathetic outflows 

 are involved. The abolition of ejaculation 

 through bilateral presacral sym})athectomy, 

 without loss of erection, has been demon- 

 strated in dogs (Van Duzen, Slaughter and 

 White, 1947) and rodents (Bacq, 1931). In 

 man and other mammals (rat, cat, and dog) , 

 the cerebral cortex inlays an important role 

 in male sexual activity (Ford and Beach, 

 1951), but an e\-aluati()n of the co-ordina- 



