MALACOSTRACA WITH SESSILE EYES. 203 



lations, of which generally the first seven have each one pair 

 of feet, and the following, and last, to the number of seven at 

 most, form a sort of tail, terminated by fins, or appendages in 

 the shape of stylets. The head presents four antennae, of 

 which the two middle are superior; two eyes and a mouth 

 composed of two mandibles, of a tongue, of two pairs of jaws, 

 and of a sort of lip, formed by two jaw-feet, corresponding to 

 the two upper ones of the decapods. As in the stomapods, 

 there exists no flagrum. The last four jaw-feet axe trans- 

 formed into feet proper, sometimes simple, sometimes termi- 

 nating in a forceps, but almost always in a single finger or 

 hook. 



According to the observations of MM. Audouin and Milne 

 Edwards, the two ganglionic cords of the spinal marrow 

 should be perfectly symmetrical, and distinct in their whole 

 length ; and according to the observations of M. le Baron 

 Cuvier, the onisci would not be remote from them, only that 

 these cords do not present in all the segments of the body 

 the same uniformity, and have some ganglia less. Thus, ac- 

 cording to them, the nervous system of these Crustacea must 

 be the most simple of all. In cymothoe and idotea the two 

 chains of ganglia would be no longer distinct. Those which 

 come immediately after the two cephalic ones would form as 

 many small circular masses, situated on the median line of 

 the body ; but the cords of communication which serve to 

 unite them together to form a continuous chain, would remain 

 isolated, and cemented one to the other. It would seem, ac- 

 cording to these facts, that these last Crustacea should be, in 

 this point of view, more elevated in the animal scale than the 

 preceding ; but other considerations appear to us strongly to 

 separate the talitri from the onisci, and to place in an inter- 

 mediate rank cymothoe and idotea. 



The sexual organs are situated inferiorly towards the origin 

 of the tail. The first two a]3pendages with which it is fur- 



