830 



FRESH-WATER BIOLOGY 



entirely different from the greenish female and young: lighter or 

 darker red. At least two species are remarkable for their striking 

 color in both sexes: one is red, the other is beautifully blue. 



The morphological characters of the Malacostraca are the follow- 

 ing: 



ant 



perp 



Fig. 1303. Diagram of a higher Crustacean. (After Caiman.) 



The body is enclosed in a comparatively hard shell, which is 

 articulated, forming a number of successive segments or somites, 

 which have a very constant number. Each somite may be com- 

 pared to a ring, which, however, is not completely circular, but the 

 upper part, called tergum or tergite, is convex, while the lower, 

 sternum or sternite, is rather fiat. The two unite on each side, 

 the tergite projecting over the sternite, and this projecting part is 

 called the pleuron. All these parts (as well as the appendages) 

 consist of a hornlike substance, called chitin, very often reinforced 

 by a considerable amount of calcareous matter. 



In the anterior part of the body we have a headpiece, to which are 

 added several more or less obscure somites that are chiefly indi- 

 cated by their appendages. As the foremost appendage we may 

 regard the eyes (e in Fig. 1303). These, however, may not be true 

 appendages. Then follow two pairs of feelers, called antennulae 

 (antl) and antennae (ant); one pair of mandibles (mand), and two 

 pairs (first and second) of maxillae (max) . 



Behind these parts the segmented body begins, including fifteen 

 somites, which all (barring reductions) bear appendages, with the 

 exception of the last, the telson (/). According to the appendages, 



