344 



CRUSTACEA. 



body, and the distal or basipodite. To the outer end of the 

 latter are articulated two usually segmented branches, an inner 

 and outer, the endopodite and exopodite respectively. The seg- 

 ments both of the protopodite and the endopodite may be 

 produced towards the median plane of the body into lobes or 

 endites (Fig. 238 a, en}. Similarly the segments of the proto- 

 podite may be produced on their outer borders into exiles, or 

 epipodites, one to three in number (ep). 



Hansen has shown that in the biramous limbs of Calanidae and Argulus 

 (the case of the Phyllopods cited by him appears less convincing) the pro- 

 topodite (or stem) is composed, not of two, but of three segments ; and this 

 he regards, with much probability, as a primitive crustacean condition. 

 When only two segments are present, the proximal segment may have 

 fused with the body (Decapods) or with the second, forming the coxopodite. 



There are some, though very few, indications of the occurrence of the 

 biramous limb in other groups of Arthropods ; e.g. the abdominal limbs 

 oiLimulus (vide infra) and the first and second maxillae of Insects. 



en- 



FIG. 238. The first (a) and second (6) left thoracic legs of Anas-pides. en endite ; end endo- 

 podite ; ep epipodites ; ex exopodite. (After Caiman.) 



The appendages of the head. The first antennae of the 

 Crustacea, the homologues, as we have seen reason to suppose, 

 of the antennae of the Myriapoda and Insects, are usually, like 

 them, simple many- jointed appendages. They are never 

 biramous in the early larval stages, though in some of the 

 Malacostraca they may acquire one (e.g. Gammarus, Fig. 239) 

 or even two (Stomatopoda, Fig. 228, and some Decapods) 

 accessory flagella. They are usually abundantly supplied with 



