248 THE MALE REPRODUCTIVE SYSTEM 



Cowper's Glands. — Cowper's glands are also known as bulbo- 

 urethral glands and are a pair of small masses located a little 

 further along the urethra from the prostate. They consist of 

 connective tissue, smooth muscle cells, and small branching com- 

 pound tubulo-alveolar glands. The walls of the glands have small 

 pockets and simple epithelium of different types lines them ; in some 

 places the cells are squamous, in others columnar. The main ducts 

 are lined with transitional or stratified columnar epithelium. Other 

 small glands occur along the course of the urethra. 



COPULATORY ORGANS. 



Lower Vertebrates. — In forms where fertilization occurs before the 

 eggs leave the body of the female there is a structural modification 

 in the male to facilitate the introduction of sperm into the female 

 reproductive system. 



In the male elasmobranch, each pelvic fin adjacent to the cloacal 

 aperture has a long finger-like process called a clasper. These two 

 structures are inserted into the cloaca of the female, and the sper- 

 matic fluid runs along the groove formed between the clasper s. 

 In some species of elasmobranchs, curved spines may l)e present 

 at the outer end of the claspers. In most fishes, fertilization is 

 external. 



In the frog, the male embraces the female and, as the latter dis- 

 charges eggs into the water, spermatic fluid is discharged from the 

 male into the water about the eggs. A unique method is found in 

 some urodeles, such as Amblystoma and Triton, where males dis- 

 charge packets of sperm, called spermatophores, formed by the 

 addition of secretions from glands in the cloacal wall. After these 

 have been discharged, the female crawls o\-er the sperm-])acket 

 until the swollen lips of the cloaca seize it and withdraw it into the 

 cloaca. 



In reptiles, a copulatory organ is present. On each side of the 

 transverse cloacal aperture, among the snakes and lizards, there is 

 a pocket in which an eversible sac lies. When these two sacs are 

 inflated and everted they form a copulatory organ, called an hemi- 

 penis. On the surface of each sac is a groove, along which si)erniatic 

 fluid passes when copulation with a female takes place. In croco- 

 diles and turtles, there is a cloacal i)enis formed from the ventral 

 wall of the cloaca. Under the epithelium of this region there is 

 loose fibroelastic connective tissue containing large vasculiir spaces; 



