30 THE TESTIS AND ITS SECKETiON 



As we descend towards the Anomoura the internal organs of 

 generation are found to give way gradually to others, which have 

 apparently a more important part to play in the economy, and 

 in the lowest forms of the Oxystoma they are in a minimum 

 state of developement. 



In this division (Brachyura) they occupy both sides of the 

 shell, lying upon the liver, and sometimes entering the folds of 

 that organ, and separated with difficulty from it. In others, as 

 Cancer and Carcinus, when in an active state, they completely 

 cover and conceal the liver. 



In Leptopodiwn and Hyas the testis is a body of considerable 

 size, lying upon the upper surface of the liver, and consisting of 

 irregular masses, formed by the twistings of its constituent duct. 

 It is covered by a delicate membrane, which is much stronger on 

 the body of the testis than elsewhere, and is analogous to the 

 tunica albuginea in the higher animals. The gland extending 

 forward, gradually enlarges, and when it has arrived in a line 

 with the stomach, curves slightly inwards to the mesial plane, 

 and terminates in a large tube on each side, which is its duct much 

 dilated. This large tube, making a number of convolutions, 

 proceeds inwards and downwards until it meets and forms a 

 junction with that of the opposite side. The anastomosis is in- 

 complete in this division of the class. After running in contact 

 for some distance the two ducts again separate, and each becom- 

 ing much smaller, terminates by opening at the base of the ex- 

 ternal organs. 



In the Anomoura, instead of being situated in the thorax, as 

 in the Bracliyura^ the testes are contained in the abdominal seg- 

 ment of the body, lying on and above the liver. They are very 

 small in all the animals of this section, the tubuli semen if eri 

 being large, and after making a few convulutions, ending in the 

 vas deferens, which opens on the base of the 5th pair of legs, 

 without the intervention of an intromittent organ. The elon- 

 gated acini are confined to the lower part, and are contained 

 within the external tunic of the gland. 



In the Macroura the testes commence on each side of the 

 stomach, and extend down to the middle parts of the abdomen. 

 In almost all the species of the section, these organs are narrow 



