16 CRUSTACEA. 



The inferior face of the brain produces four nerves, which 

 belong to the antennae, and that also give off some twigs to the 

 neighbouring parts. Two nervous and very long cords, em- 

 bracing the esophagus laterally and uniting beneath it, arise 

 from its posterior margin. There, as in the Brachyura, this 

 union only takes place in the middle of the thorax, the me- 

 dulla then assuming the form of a ring whose proportions are 

 eight times larger than those of the brain : six nerves on each 

 side arise from this ring : the anterior ones belong to the parts 

 of the mouth, and the five others to the five feet of the same 

 side. From the posterior margin arises another nerve which 

 runs to the tail, without producing any sensible ganglion, and 

 that apparently represents the ordinary nervous cord. Here, 

 as in the Macroura, each of the two nervous cords, previous 

 to uniting beneath the esophagus, and at about the middle of 

 its length, gives off a thick nerve for the use of the mandibles 

 and their muscles. United, they form a first — sub-cervical — 

 ganglion that distributes nerves to the maxillae and the foot- 

 jaws(l); they afterwards continue approximated throughout 

 their length, presenting eleven successive ganglions, each of 

 the five first furnishing nerves to as many pairs of feet, and 

 the remaining six those of the tail; that of the Pagurus has 

 some ganglions less, thus appearing to form the passage from 



the Brachyura to the Macroura. M. Serres thinks that he 



has recognized in these Decapoda, vestiges of the great sym- 



pathetic(2). 



The lateral margin of the shell is bent under, to cover and 



protect the branchiae, leaving an opening anteriorly for the 



(1) According to M. Straus, the anlerior division of the body of the Limuli, 

 that which is covered by a semi-lunar buckler, presents, besides the brain, no 

 other ganglion but this, whence we may infer that the inferior organs of locomo- 

 tion correspond to the parts of the mouth in the Decapoda, Stomapoda, and even 

 in the Arachnides, and that those of the other division of the body, or of the 

 second buckler, are analogous to the feet of the same Decapoda. 



(2) Messrs Audouin and Edwards have observed in the Maia and in the Palinu- 

 rus a nerve analogous to the one called by Lyonet, in his Jinatomie de la Chenille 

 du Saule, "recurrent." The discovery of the other gastric nerves is also due to 

 them. 



