86 CRUSTACEA. 



ganglions which immediately follow the two cephalics, form 

 as many small circular masses situated on the median line of 

 the body; but the cords of communication w.hich serve to 

 connect them, remain isolated and attached to each other. It 

 would appear from these facts that the latter Crustacea are 

 higher in the animal scale than the preceding ones, but other 

 considerations seem to us to require a considerable separation 

 between the Talitri and Onisci, and the arrangement of the 

 CymothotC and Idotese in an intermediate rank. 



The organs of generation are situated inferiorly near the 

 origin of the tail. The two first appendages with which it is 

 furnished beneath, and which are analogous to those presented 

 to us by the same part in the preceding Crustacea, but more 

 diversified, and always, as it appears, supporting the bran- 

 chiae, differ in this respect, according to the sex. The coitus 

 takes place like that of insects, the male placing himself on the 

 back of his female ; the latter carries her ova under the thorax, 

 between scales which form a sort of pouch. There they are 

 developed, and the young remain attached to the feet or 

 other parts of the body of their mother, until they have ac- 

 quired the strength requisite for natation, and providing for 

 their wants. All these Crustacea are small, and mostly in- 

 habit the sea-coast or fresh water. Some are terrestrial, 

 and others are known which are parasitical. 



They are divided into three orders : those whose mandibles 

 are furnished with a palpus, appear to be naturally connected 

 with the preceding Crustacea such are the Amphipoda ; 

 those in which these organs are deprived of them will consti- 

 tute the two following orders the Lsemodipoda and the Iso- 

 poda. The Cyami, a genus of the second one, being parasi- 

 tical, naturally lead us to the Bopyri and Cymothoae, with 

 which we commence the Isopoda. 



