186 TRANSPORTATION OF THE GAMETES 



females. It is to be observed in this connection that Mann ('49) gives the 

 amount of ejaculate in the cock as 0.8 cc, highly concentrated with sperm. 



Another variation found in certain birds is the presence of a seminal vesicle 

 located at the caudal end of the reproductive duct. This outgrowth is a sperm- 

 storage organ and is not comparable to the secretory seminal vesicle found 

 in mammals. Such seminal vesicles are found in the robin, ovenbird, wood 

 thrush, catbird, towhee, etc. These structures enlarge enormously during the 

 breeding season, but in the fall and winter months they shrink into insignificant 

 organs (Riddle, '27). It is apparent that the seminal fluid is moved along 

 and stored at the distal (posterior) end of the reproductive duct in these 

 species. Other birds, such as the pigeon and mourning dove, lack extensively 

 developed seminal vesicles, but possess instead pouch-like enlargements of 

 the caudal end of the reproductive duct when the breeding season is at its 

 maximum. 



In many lower vertebrates which practice internal fertilization, large seminal 

 vesicles or enlargements of the caudal end of the reproductive duct are present. 

 Such conditions are found in the elasmobranch fishes. These structures act as 

 sperm-storage organs during the breeding season. 



3. Transportation of Sperm from the Testis in Vertebrates 

 Possessing a Relatively Simple Reproductive Duct 



In forms such as the frog, toad, and hellbender (figs. 9, 105C), the pressure 

 within the seminiferous tubules of the testis associated with contractions of 

 the reproductive duct serve to move the sperm along the reproductive duct. 

 At the time of spawning, a copious discharge of sperm is effected. In teleost 

 fishes, a general contraction of the testicular tissue and the muscles of the 

 abbreviated sperm duct propel the sperm outward during the spawning act 

 (fig. 105D). In teleosts, sperm are stored in the testis, or as in the perch, 

 large numbers may be accommodated within the reproductive duct (fig. 105D). 

 Slight motility also may be a factor in effecting sperm transport down the 

 reproductive duct in the lower vertebrates. 



C. Transportation of Sperm Outside of the Genital Tract of the Male 



1. Transportation of Sperm in the External Watery Medium 



In most teleost fishes and in amphibia, such as the frogs and toads, and 

 the urodeles of the families Hynobiidae and Cryptobranchidae (possibly also 

 the Sirenidae), fertilization is external and sperm are discharged in close 

 proximity to the eggs as they are spawned. Many are the ways by which this 

 relationship is established, some of which are most ingenious (fig. 103). 

 Sperm motility, once the watery medium near the egg is reached, brings the 

 sperm into contact with the egg in most instances. However, exceptional cases 

 are present where the sperm are "almost completely immobile," such as in 



