80 CRUSTACEA. 



a single piece, which however is free behind, usually exposing 

 the thoracic segments, bearing the three last pairs of feet and 

 having an articulation before that serves as a base to the eyes 

 and intermediate antennae ; these latter organs are always ex- 

 tended and terminated by two or three threads. The eyes 

 are always approximated. The formation of the mouth is 

 essentially the same as in the Decapoda ; but the palpi of the 

 mandibles, instead of being laid on them, are always vertical. 

 The foot-jaws are deprived of the ilagelliform appendage pre- 

 sented to us by the same parts in the Decapoda. They have 

 the form of claws or of small feet, and, at least in several — 

 the Squiilai, — their external "base as well as that of the two 

 anterior feet properly so called, exhibits a vesicular body. 

 Those of the second pair, in the same Stomapoda, are much 

 larger than the others and even than the feet, which has caused 

 them to be considered as true feet ; fourteen of them have 

 been counted(l). The four anterior feet have also the form 

 of claws, but are terminated as well as the foot-jaws by a hook 

 which curves towards tlie head, on the inferior and ante- 

 rior edge of the preceding joint or of the hand. In others how- 

 ever — the Phyllosoma for instance(2) — all these organs are 

 filiform and have no forceps. Some of them at least, as well 

 as the last six and equally simple ones of the Stomapoda pro- 

 vided with claws, have an appendage or lateral branch. The 

 seven last segments of the body,' containing a large portion of 

 the heart and furnishing a base for the attachment of the res- 

 piratory organs, can no longer in this respect be assimilated 

 to that portion of the body which is called the tail in the De- 

 capoda : it is a true abdomen. Its penultimate segment has 

 a fin on each side formed like the caudal of the Macroura, 

 but is frequently, as well as the last segment or intermediate 

 portion, armed with spines or teeth. 



(1) The second jaws of these Stomapoda no longer present the same form as 

 those of the Decapoda. They have the figure of an elongated triangle divided 

 into four segments by transverse lines. The mandibles are bifurcated and well 

 dentated. 



(2) In all those where the four anterior feet are in the form of claws, the six last 

 are natatory. 



