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tubes passing- backward from the testes to the posterior 

 region of (lie thorax, where each opens to the exterior on 

 (he coxopodite of the last walking leg. 



In a mature crab the course of each of the vasa 

 deferentia is as follows :— Where it arises from the inner 

 portion of the main lobe of the testis the vas deferens is 

 an extremely convoluted and narrow tube. As it sweeps 

 round the outer side of the cardiac stomach the tube 

 grows broader and the convolutions become less compli- 

 cated, so that in this region the course of the vas deferens 

 may be traced without much difficulty. At the level of 

 the pyloric fore-gut the duct turns suddenly inwards and 

 covers the lateral walls of this region of the alimentary 

 canal. From this point the vas deferens passes backward 

 as a white convoluted tube above the hind-gut and below 

 the pericardium. The maximum width is attained below 

 the anterior region of the heart. Behind this point the 

 duct gradually becomes narrower, and is then known as 

 the ejaculatory duct [e. <!.). At the posterior end of the 

 pericardium the duct dips downward through the foramen 

 on the outer side of the " sella turcica." It then passes 

 behind the dorsal extensor muscle of the coxa of the last 

 walking leg and in front of the extensor muscle of the 

 basi-ischium of the same appendage. Below the latter 

 muscle it passes beneath the flexor of the basi-ischium, 

 and opens to the exterior at the end of a soft papilla 

 situated on the ventral surface of the coxa of the last 

 walking leg. 



In sections through the testis the gland is seen to be 

 composed of numerous follicles which are closely packed 

 together. Each follicle is lined by epithelial cells which 

 surround a central cavity, and this cavity is continuous 

 with that of the vas deferens. In an early stage the cells 

 of the follicles are not differentiated and are quite small. 



