784 



CRUSTACEA. 



accustomed to look upon the members of the 

 first and second abdominal rings as the ex- 

 ternal male instruments. These two pairs of 

 extremities, in fact, (Jig. 433), are distinguished 



Fig. 433. 



Members of the first and 

 second abdominal rings of 

 the Male Ma$a. 



from the rest by their shape, which is styli- 

 form, and their structure, which is tubular, 

 being composed of two horny laminae convo- 

 luted one upon another, the first including 

 the second. But direct observation has de- 

 prived them of all claim to be considered as 

 fulfilling any office of so much consequence in 

 the economy of the Crustacea as that of con- 

 veying the fecundating fluid from the body of 

 male into that of the female. At the most, 

 they can only be regarded as organs of excita- 

 tion, and which the animal may perhaps em- 

 ploy at the same time to guide the male into 

 the female organ. 



The female reproductive apparatus of the 

 Crustacea, in its highest state of complication, 

 onsists of an ovary, an oviduct, and copulatory 

 pouches. 



Fig. 434. 



Female organs of the Maja Squinado. 



The ovaries in the Decapoda brachyura resem- 

 ble four cylindrical tubes (a, b,jig. 434) placed 

 longitudinally in the thorax, and divided into 

 two symmetrical pairs, each opening into a 

 distinct oviduct, yet communicating with one 

 another by a transverse canal ('), and by 

 the intimate union of the two posterior tubes 

 in a portion of their length (6'). The ovi- 

 ducts, as well as the ovaries, are of a whitish 

 colour; they are short, and become united 



in their course to a kind of sac (c), the neck 

 of which extends to the exterior of- the ani- 

 mal's body (d); there is one of these on 

 each side, and they are known by the name of 

 the copulatory pouches. It is into these reser- 

 voirs that the male pours the fecundating fluid, 

 which is here stored up and applied to the 

 ova as they pass in succession along and out 

 of the oviducts. These, after a course which 

 is never long, terminate at the vulvse, openings 

 formed in the sternal pieces of the segment 

 which supports the third pair of ambulatory 

 extremities. 



The Anomoura and Macroura have no copu- 

 latory pouches, and their vulvae are situated 

 on the basilar joint of the ambulatory ex- 

 tremities of the third pair. The mode in 

 which fecundation is accomplished in these 

 genera is consequently much less apparent 

 than in the Brachyura. Many writers are 

 of opinion that this operation takes place in 

 the interior of the ovaries, a process that 

 appears by no means feasible on account 

 of the inequality of development of the ova, 

 which is such, that the last of them are not in 

 being even long after the first have been ex- 

 pelled. It would perhaps be more correct to 

 suppose that fecundation does not take place 

 till after the ova are laid, which we know to be 

 the case among the Batrachia and the greater 

 number of fishes. 



The female Crustacean does not abandon her 

 eggs after their extrusion. Those of the Deca- 

 pods preserve them under their abdomen by 

 means of the abdominal extremities modified 

 Fig. 435. in their structure (Jig. 390 and 

 435); the Edriophthalmia, 

 again, keep them under their 

 thorax by means of the fla- 

 belliform appendages of the 

 extremities belonging to this 

 region (Jig. 436); whilst the 

 inferior genera, such as the 

 Entomostraca, &c. have sus- 

 pended to the external orifices 

 either horny tubes or a 



Ventral aspect of the female 

 Cymothoa. 



p, legs ; f, flabelliform ap- 

 pendages which unite so 

 as to form a cavity des- 

 tined to contain the ova. 



