THE DECAPODA 



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Reproductive System. The testes as a rule lie partly in the 

 thoracic region and partly in the abdomen, and, except in some 

 Paguridae, are connected with each other across the middle line. 

 In the simplest cases, as in some Caridea, they are tubular in form, 

 but as a rule they send off numerous caecal diverticula. In 

 Leucifer the two testes unite with each other to form an unpaired 

 mass lying below the intestine. In the Paguridae they are dis- 

 placed backwards so as to lie wholly in the abdominal region, where 

 they are unsymmetrically placed on the left side, either fused into 

 a single mass or entirely separated from each other, the right testis 

 lying in front of the left. 



The vas deferens presents typically three divisions (which, 

 however, are not distinctly defined in many Caridea) : (1) a narrow 



Fid. 168. 

 Aristeus coruscans (Penaeidae). (Prom Alcock, Naturalist in Indian Seas.) 



efferent duct leading from the testis ; (2) a glandular part, with 

 wider lumen, often convoluted ; (3) a terminal ductus ejaculatorius 

 with muscular walls. In Brachyura (except Dromiidae) the distal 

 portion of the second or glandular division is provided with caecal 

 diverticula which in some cases are very numerous, forming a large 

 glandular mass. In Leucifer the structure of the vas deferens is 

 very complex, and there are two distinct glandular regions. 



In nearly all cases the terminal portion of the vas deferens 

 perforates the coxopodite of the last pair of legs, or emerges on the 

 arthrodial membrane between the coxopodite and the body. In 

 the majority of cases no penes are formed, but in some genera of 

 Paguridae (Spiropagurus, etc.) a membranous tubular penis is present 

 on one side only. In all Brachyura a pair of penes are present, 

 the tips of which lie within the grooves of the first pair 'of 

 abdominal appendages. In those families of Brachygnatha formerly 



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