318 



PHYSIOLOGY OF GONADS 



rete and mnning such a constant zigzag 

 course within the testis that a palisade is 

 formed. An average tubule is 30 cm. long. 

 The tubules do not end blindly as a rule. 

 They rarely fork or bifurcate and they 

 never communicate with one another (Mlil- 

 ler, 1957; Clermont. 1958). 



The suitability of architecture of the 

 tubule for the process of spermatogenesis 

 is obvious because it provides an epithe- 

 lium with a large surface area. The arrange- 

 ment of the tubules in arcs and palisades 

 allows long tubules to be packed neatly in 

 a small, ovoidal organ. The lumen of the 

 tubule constitutes a pathway for the trans- 

 port of sperm to the outside. Because sperm 

 cells are transported passively, some mobile 

 medium is needed. The obvious medium 

 is fluid which can be transferred along the 

 length of the tulnile. It is not known where 

 and how such fluid enters the tubule and 

 how it moves through the lumen as it trans- 

 liorts sperm to the ductuli efferentes. 



If fluid moves constantly along the length 

 of the tubule to carry sperm, it must be re- 

 absorbed from the excretory duct system. 

 The ductuli efferentes, derived from the 

 mesonephros, may play a role analogous 

 to that of a nephron in reabsorbing large 

 ciuantities of fluid from the seminiferous 

 tubules (Ladman and Young, 1958). The 

 cytologic organization of ciliated and non- 

 ciliated cells in the ductuli efferentes and 

 rete testis of the guinea pig seems compat- 

 ible with the presumption that these cells 

 absorb fluid from the lumen and excrete 

 it by way of the ductular system. Physio- 

 logic evidence of the transport of fluid 

 within the excretory duct system will l)e 

 given in Section VIII. 



The architecture of the interstitium ap- 

 pears to be well adapted for the internal 

 secretory function of the Leydig cells. 

 Wedges of connective tissue are present in 

 the interstices bounded by three tubules. 

 The wedges contain Leydig cells, blood 

 vessels, and connective tissue. Branches of 

 the testicular artery feed the capillary net- 

 work in the connective tissue wedges. The 

 wedge capillaries are in close relationship 

 to the Leydig cells. The topography of the 

 capillary system of the rat testis is such 

 that blood, after contact with the intersti- 

 tial cells, flows by the g('nerati\'c portion 



of the testis before entering the general 

 circuation through the great veins at the 

 hilum. This architecture apparently makes 

 it feasible for hormones of the Leydig cells 

 to exert local action on the tubule. 



VI. The Circulatory System 

 of the Testis 



The testicular artery of mammals con- 

 volutes before reaching the testis. It is sur- 

 rounded by the pampiniform plexus which 

 is thermoregulatory, serving to preheat or 

 to precool the blood. The convolutions of 

 the testicular artery constitute a distinctive 

 feature of mammals (Fig. 5.6). Lower ver- 

 tebrates have segmental arteries, the testes 

 do not descend, and the arteries do not 

 lengthen or convolute. Marsupials differ in 

 that the artery forms a rete marabile from 

 which a short artery enters directly into 

 the testis. The testicular artery in the dog 

 forms 25 to 30 loops before entering the 

 tunica albuginea. In the goat, the artery 

 convolutes many times but finally branches 

 into 3 or 4 convolutions that enter the testis 

 from all sides. The testicular artery in the 

 mouse has half-loops; except for man, it 

 shows the fewest convolutions of all the 

 mammalian testicular arteries thus far in- 

 vestigated by arteriography. The situation 

 in the monkey is similar to that in the dog, 

 whereas the artery in the cat and the 

 guinea pig has between 5 and 10 loops. 



The testicular artery of man is unique 

 in two respects. It is the longest and thin- 

 nest artery in all the viscera, and it is also 

 the straightest testicular artery in the 50 

 mammals thus far investigated. The testic- 

 ular artery of man after giving off branches 

 to the cord and epididymis generally runs 

 on the posterior border of the testis. It 

 bifurcates, each branch penetrating the 

 tunica over its lateral and medial aspects 

 (Harrison and Barclay, 1948). The testicu- 

 lar artery in man has a direct anastomosis 

 with the vasal and cremasteric arteries 

 (Harrison, 1948a, b; 1949a, b; 1952; 

 1953a, b). 



The gradient in temperature between the 

 i:»eritoneal and scrotal cavities varies widely 

 among different species. A large gradient 

 ocelli's in the goat, rabbit, rat, mouse, and 

 ram ; a small gradient is i)resent in the mon- 

 key, (log, guinea pig. and man. The tcm- 



