CRUSTACEA. 85 



MALACOSTRACA. 



b. Eyes sessile and immovable. 



The Branchiopoda are the only Crustacea of which we shall 

 henceforward have occasion to speak, that exhibit eyes placed 

 on pedicles. But independently of the fact that these pedi- 

 cles are neither articulated nor lodged in special cavities, the 

 Branchiopoda have no shell and are otherwise removed from 

 the preceding Crustacea by various characters. All the Ma- 

 lacostraca of this division are also deprived of a shell ; their 

 body, from the head downwards, is composed of a suite of 

 articulations of which each of the first seven is furnished 

 with a pair of feet, the following and last ones, seven at most, 

 forming a sort of tail terminated by fins or styliform appen- 

 dages. The head presents four antennae, the two interme- 

 diate superior, two eyes, and a mouth composed of two man- 

 dibles, a tongue, two pairs of jaws, and a sort of lip formed 

 by two foot-jaws that correspond to the two superior ones of 

 the Decapoda ; here, as in the Stomapoda, the flagrum no 

 longer exists. The four last foot-jaws are transformed into 

 feet, sometimes simple and at others constituting a claw, but 

 almost always with a single toe or hook. 



According to the observations of Messrs Audouin and Ed- 

 wards, the two ganglionary cords of the spinal marrow are 

 perfectly symmetrical and distinct throughout the whole of 

 their length, and from those of the Baron Cuvier it would ap- 

 pear that the Onisci are only removed from them because 

 these cords do not present the same uniformity in all the seg- 

 ments of the body, and because there are some ganglions 

 less(l). Thus, according to them, the nervous system of the 

 Crustacea is the simplest of all ; in the Cymothoae and Idoteae 

 the two ganglionary chains are no longer distinct, and those 



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(1) See Oniscus. 



