CRUSTACICA. 



155 



FIRST GENERAL DIVISION. 



MALACOSTRACA. 



The Malacostraca naturally divide themselves into those whose eyes 

 are placed on a movable pedicle, and those in which they are sessile 

 and fixed. 



a. Eyes jjlaced on a movable and articulated j^edicle. 



Eyes* placed on a movable pcdi:;le composed of two articulations, 

 and received into fossulee, distinguish the Decapoda and Stomapoda 

 from all the others. Anatomically considered, they appear to be still 

 further removed from them, — Le9ons d'Anat. Compar., Cuv. ; Ann. 

 des Sc. Nat., t. XI, — inasmuch as they are the only ones that present 

 sinuses in which the venous blood is collected previous to its trans- 

 mission to the branchiae on its return to the heart. 



The Decapoda and Stomapoda resemble each other in several cha- 

 racters common to both. A large plate, called a shell, covers a 

 greater or less extent of the anterior portion of their body. They all 

 have four antennae f , the middle ones of which are terminated by two 

 or three filaments ; two mandibles, each of which, at its base, bears a 

 palpus that is divided into three joints, and usually laid on it; a bilo- 

 bate tongue ; two pairs of jaws ; six foot-jaws, the four posterior of 

 which, in some, are transformed into claws ; and ten feet, or fourteen, 

 in those where the four foot-jaAVS have that form. 



In the greater number the branchiae, of which there are seven 

 pairs, are concealed under the lateral margin of the shell; the two 

 anterior pairs are situated at the origin of the four last foot-jaws, and 

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



* Behind the cornea, according to Blainville, is a choroides perforated with nume- 

 rous holes; then a true crystalline, resting on a nervous ganglion, and divided into 

 a multitude of little fasciculi. 



t "V^'e must distinguish the peduncle — stipes, — p.nd the stem — caulisfunicidis. The 

 peduncle is thicker, cylindrical, and composed of tlnee joints, a numher which seems 

 peculiar to these organs in their imperfect or rudimentary state. The stem is seta- 

 ceous, and divided into a variable number of very small joints. That of the exter- 

 nal antennfe is simple, but that of the interior ones, consists of at least two filaments, 

 and in several of the Decapoda IMacroura, of three. Passing gradually from these 

 latter to the Brachyura, the antennae become shortened, so that, in several of the 

 Quadrilatera, the lateral ones, at least, are very small. In this case the two termi- 

 nal divisions of the intermediate ones form a sort of bifurcated forceps, or unequal 

 and articulated fingers. 



