654 ANATOMY OF VERTEBRATES. 



aggregate groups of cseca. The Cowperian glands resemble 

 those of Castor. A pair of long thin glandular bodies opening 

 into the prepuce, on each side the glans, ib. a, answer to the chief 

 castor-bags, c,f, fig. 607, in the Beaver: the homologues of g — k, 

 fig. 508, are confluent and surround the termination, fig. 510, v, 



Protometra and prostates, Beaver. (Part of PI. vi. ccxxxvm".) 



of the rectum s, and exude their opaque whitish secretion near 

 the anus. 



In the Marmots (Arctomys) the preputial orifice is more dis- 

 tinct than in most Rodents from that of the rectum : in the Alpine 

 marmot the space of an inch intervenes. The prostates form a 

 considerable mass, aggregated into two roundish lobes. The 

 mesorchial accumulation of fat is considerable at the commence- 

 ment of hibernation. The vesicular glands of the Jerboa (Dipus 

 sagitta) resemble those of the Vole, but are less notched. In 

 Helamys capensis, they consist of slightly sacculate pendulous 

 bags, with thin walls : the prostatic follicles are numerous, short, 

 and thick: the glans penis becomes singularly expanded, and 

 forms a hollow disc in the centre of which opens the urethra. 



In the Rat and Mouse the periodical enlargement of the testes, 



