ACCESSORY MAMMALIAN REPRODUCTIVE GLANDS 



877 



of a specialized gland (the prostate) from 

 simpler glands which are nmnerous along 

 the urethra. The probable evolution of pros- 

 tates and bulbo-urethral glands from 

 smaller, simpler urethral glands has been 

 suggested in the past. Observations of 

 Bruner and Witschi (1946) support this 

 concept. In experiments on fetal hamsters, 

 it was found that masculinized females de- 

 veloped prostate glands but the ducts 

 joined the collecting ducts of the urethral 

 glands and did not open directly into the 

 urogenital sinus. According to these work- 

 ers, this may represent an intermediate 

 stage in the development of specialized 

 glands. 



The history of the cloaca may well be im- 

 portant in relation to development of acces- 

 sory glands (Retief, 1949). The cloaca is 

 retained in modern reptiles; in monotremes 

 it is subdivided cranially into ventral uro- 

 deum or urogenital sinus and a dorsal copro- 

 deum; it is represented by a pocket in mar- 

 supials but is lost as a discrete structure in 

 all higher mammals. The first development 

 of a separate urogenital duct or urethra as 

 it occurs in monotremes may be correlated 

 with the first appearance of discrete acces- 

 sory glands from this specific region in 

 mammals. 



The marsupials illustrate a more ad- 

 vanced type of glandular development with 

 three histologically distinguishable regions 

 in the disseminate prostate and three pairs 

 of bulbo-urethral glands. Seminal vesicles 

 and ampullary glands are found only among 

 higher mammals. 



The size and structural complexity of 

 these unique glands in mammals raises the 

 question of the adaptive value of relatively 

 large accessory glands associated with the 

 mammalian reproductive tract. This is a 

 matter only for speculation. The evolution 

 of such glands with increased surface for 

 secretion and enlarged storage space may, 

 perhaps, have been correlated with a tend- 

 ency for an increase in volume of seminal 

 plasma in the ejaculate of mammals. Mann 

 (1954a) pointed out the variability in the 

 volume of ejaculated semen and in the 

 sperm density in various species. With re- 

 gard to the volume of seminal plasma, he 

 stated, "In lower animals it may be so 

 scarce that the emitted semen takes the 



form of a very thick lump of spermatozoa, 

 closely packed together. There is little semi- 

 nal plasma in bird semen and even among 

 some of the mammals, but on the whole, the 

 higher mammals including man, produce a 

 relatively dilute semen with a considerable 

 l)roportion of seminal plasma." A second 

 suggestion, more speculative, is that the 

 evolution of large mammalian glands may 

 also have compensated for loss of accessory 

 reproductive function in the kidney. The 

 kidney of mammal-like reptiles and ances- 

 tral mammals may have contributed to the 

 formation of seminal plasma (as is true in 

 modern reptiles, amphibians, and fishes), 

 but the compact kidney of warm-blooded, 

 metabolically active mammals may be ill 

 adapted for such a purpose. 



II. Function of the Male 

 Accessory Glands 



A. INTRODUCTION 



The only known function of the male ac- 

 cessory glands is to secrete the seminal 

 plasma. The proportion of this fluid which 

 originates from the various secretory or- 

 gans, or even from different lobes of the 

 same gland, varies greatly from one species 

 to another. There is also remarkable species 

 variation in the volume and composition of 

 the individual secretions. The functional 

 activity of the accessory glands is governed 

 primarily by hormones of testicular origin. 

 The output of androgens is subject to the 

 control of the anterior hypophysis, and 

 many factors (e.g., age, light, season, tem- 

 perature, and diet) affect the secretory ac- 

 tivity of the hypophysis and testis. Thus, it 

 is not surprising that in a given individual, 

 there may be marked fluctuations in the 

 cjuantity and chemistry of the secretions of 

 the accessory glands, and hence of the semi- 

 nal plasma. 



The development by Charles Huggins of 

 ingenious surgical procedures enabled the 

 secretory activity of the canine prostate to 

 be measured by simple volumetric methods. 

 Such studies of prostatic secretion in the 

 dog established the quantitative relation- 

 ships between the function of prostatic epi- 

 thelium and the androgenic status of the 

 host. In other species, serial collection of the 

 individual secretions in the same animal 



