CRUSTACEA. 



345 



complete separation which exists between the organs belonging to the 

 two sides of the body; for not Fig. 162. 



only are the internal secret- 

 ing viscera for the most part 

 perfectly distinct from each 

 other, but even the external 

 sexual orifices are equally se- 

 parate and unconnected. 



(382.) Beginning with the 

 parts observable in the male, 

 we will take the cray-fish ( As- 

 tacusjluviatilis)as a standard 

 of comparison, and briefly 

 notice the principal variations 

 from the type of structure, 

 observable in that species, 

 met with in other genera. 



In the cray-fish and also 

 in the lobster, the secerning 

 organs or testes, when exa- 

 mined in situ, are found to occupy the dorsal region of the thorax, 

 lying upon the posterior part of the stomach. 



Examined superficially, the testes would seem to form but one 

 mass consisting of three lobes (fig. 162, a, a, b) ; but, on investi- 

 gating the minute structure of the organ, it is found to be made up 

 of very delicate -secreting tubes that give origin to two excretory 

 ducts (c, c). After numerous convolutions, which form a kind of 

 epididymis (c?), each duct, becoming slightly dilated, terminates by 

 a distinct orifice (/), seen upon the basal articulations of the last 

 pair of ambulatory legs. There is no intromittent apparatus visible ; 

 but, according to Milne Edwards,* the extremity of the excretory 

 duct, by undergoing a kind of tumefaction, may be protruded exter- 

 nally, so as to become efficient in directing the course of the fecun- 

 dating fluid. 



In crabs the mass of the testis is exceedingly large, but in its 

 essential structure similar to that of the cray-fish, and the external 

 opening of its excretory duct is found to occupy the same situation : 

 in some genera, however, instead of being placed upon the first 

 joint of the last pair of legs, the orifices of the male organs are 

 found upon the abdominal surface of the last thoracic ring itself. 



* Cyclop, of Anat. and Phys. art. CRUSTACFA. 



