18 THE TESTIS AND ITS RELATION TO REPRODUCTION 



externally by means of two abdominal pores. Each pore empties into the 

 urogenital sinus. In teleost fishes (perch, flounder, etc.) the conveying repro- 

 ductive duct is a short, simple tube continuous with the testis at its caudal 

 end and passing posteriorly to the urogenital sinus (fig. 9A). In frogs and 

 toads, as well as in certain other fishes, such as Amia and Polypterus, the 

 male reproductive duct is a simple, elongated tube associated with the testis 

 by means of the eff'erent ductules of the latter, coursing posteriad to open 

 into the cloaca (frogs and toads) or to the urogenital sinus (Amia; Polypterus) 

 (fig. 9B, C). Simplicity of sperm duct development and external union of 

 the gametes are associated reproductive phenomena in the vertebrate group. 



b. The Reproductive Duct in Species Practicing Internal Fertilization 



An entirely different, more complex male reproductive duct is found (with 

 some exceptions) in those vertebrates where gametic union occurs within 

 the protective structures of the maternal body. Under these circumstances 

 there may be a tendency for one male to serve several females. Enlargement 

 of the duct with the elaboration of glandular appendages, and structures or 

 areas for sperm storage is the rule under these conditions (fig. 9D-F). This 

 form of the male genital tract is found not only in those species where an 

 intromittent organ deposits the sperm within the female tract, but also where 

 the sperm are deposited externally in the form of spermatophores (fig. 10). 



In many species, the reproductive duct is greatly lengthened and becomes 

 a tortuous affair, especially at its anterior or testicular end. In fact, the cephalic 

 end of the duct may be twisted and increased to a length many times longer 

 than the male body itself. This coiled, cephalic portion is called the duct of 

 the epididymis (epididymides, plural). (See figs. 7, 9E.) The word epididymis 

 is derived from two Greek words: epi = upon, and didymis = testicle. The 

 epididymis, therefore, is the body composed of the tortuous epididymal duct 

 and the efferent ducts of the testis which lie upon or are closely associated 

 with the testis. The complex type of reproductive duct is composed thus of 

 two main portions, an anterior, contorted or twisted portion, the epididymal 

 duct, and a less contorted posterior part, the vas deferens or sperm duct 

 proper (fig. 9D, E). 



In some vertebrates, in addition to the above complications, the caudal 

 end of the reproductive duct has a pronounced swelling or diverticulum, the 

 seminal vesicle (e.g., certain sharks and certain birds). The latter structures 

 are true seminal vesicles in that they store sperm during the reproductive 

 period. 



The epididymal duct in man is a complex, coiled canal composed of a head 

 (caput), a body (corpus), and a tail (cauda). (See fig. 7.) It is C-shaped 

 with its concavity fitting around the dorsal border of the testis, the head 

 portion being located at the anterior end of the latter. The total length of 

 the epididymal duct in man is said to be about 4 to 7 m. In other mammals 



