CLASS CRUSTACEA. 139 



MALACOSTRACA WITH EYES SUPPORTED ON A MOVE- 

 ABLE AND ARTICULATED PEDICLE, OR DECAPODA 

 AND STOMAPODA IN GENERAL. 



Eyes supported on a mobile pedicle, of two articulations, 

 lodged in fossets, distinguish these Crustacea from all others. 

 Considered anatomically, they appear to be still more remote 

 from them, inasmuch as they are the only ones which present 

 sinuses where the venous blood collects, before repairing to 

 the gills to return to the heart. 



The decapoda and stomapoda resemble each other in many 

 common characters : a large shell, sometimes divided in two, 

 called testa or carapace, covers in front a more or less ex- 

 tended portion of the body. They all have four antennae, of 

 which the middle are terminated by two or three threads ; two 

 mandibles, with a palpus near the base of each, divided into 

 three articulations, and usually inclined upon the mandibles ; 

 a bilobate tongue ; two pair of jaws ; six jaw-feet, but the four 

 posterior of which are in some transformed into claws ; ten or 

 fourteen feet, in those in which the four jaw-feet have this 

 form. 



In the greater majority, the gills, seven pair in number, are 

 concealed under the lateral edges of the testa ; the two ante- 

 rior pair are situated at the origin of the last four jaw-feet, and 

 the others at that of the feet properly so called. In the other 

 cnistacea, they are annexed, under the form of tufts, to five 

 pairs of feet like fins, situated under the post-abdomen ; the 

 under part of this posterior portion of the body is equally 

 furnished in the others with four or five pairs of bifid 

 appendages. 



