iZ CRUSTACEA. 



FIRST GENERAL DIVISION. 



MALACOSTRACA. 



The Malacostraca naturally divide themselves into those 

 whose eyes are placed on a movahle pedicle, and those in which 

 they are sessile and fixed. 



a. Eyes placed on a movable and articulated pedicle. 



Eyes(l) placed on a movable pedicle composed of two arti- 

 culations, and received into fossulse, distinguish the Decapoda 

 and Stomapoda from all tlie others. Anatomically considered, 

 they appear to be still further removed from them, — Legons 

 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 transmission to the 

 branchice on its return to the heart. 



The Decapoda and Stomapoda resemble each other in se- 

 veral characters 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 antennse(2), the middle ones of 



(1) Behind the cornea, according to Blainville, is a choroides perforated with 

 numerous holes; thenatrue crystaUine, resting on a nervous ganglion, and divided 

 into a multitude of little fasciculi. 



(2) We must distinguish the peduncle — s^/pes,— and the stem— caulis, funiculus. 

 The peduncle is thicker, cylindrical, and composed of three joints, a number which 

 seems pecuhar to these organs in their imperfect or rudimentary state. The stem 

 is setaceous, and divided into a variable number of very small joints. That of the 

 external antennae is simple, but that of the interior ones consists of at least two 

 filaments, and in several of the Decapoda Macroura, of three. Passing gi-adually 

 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 terminal divisions of the intermediate ones form a sort of bifurcated forceps, 

 or unequal and articulated fingers. 



