3ii0 



ARTHROrODA 



capillaries, and veins are well de\-eloped, luit wilh ihe dilTnsc respiraliou 

 onlv the heart persists as a rediieed structure, or with its i.lisappearauce 

 the last traces oi a circidat(ir\" s\"stent are lost. 



Locomotion is also rel.ited to the aquatic life anil these animals usually 

 possess appendages of the birainous or si'hizopoJjl type, which at ouce 





Fio. j;74. — Cojiepod appendages. 7— /T", Phil^fonnis castor: I, a i^iUT oi ^>:\uzo[K^di\l 

 feet: //, second right antenna; ///, vighl niandiliie; I]', right niaxIUa; T, riglil mandible 

 of Cyclops coronalus. i, 2, joints of basiopodite; /, entiopodite; o, exopoditc. 



dilTerentiates these forms from all other artltropods. Wliile irt the latter, 

 as e\'cry insect shows, the joints of the limh are in a single row, the crus- 

 tacean appemlage has a two-jointed base (basiopihlilc), followed In' two 

 many-jointed branches (llg. 374, /), an iitner or ciiJopoditc anil an 

 outer or cxopoili/c. 



Fig. 375.—/ and // first and sixlli legs of Broiuiil/^iis xriihci (after Oerstiieker). 

 a, llabellum; h, basis; /, axon and its cndiles; k. gills. 



The schizopodal appendage occurs only when the limh is used for swimming; 

 when it is used for walking, as in crayfish and crabs, the e.xopodite is lost and 

 only the cndopoditc persists as the fmictional linili, which (hen closely resembles 

 the appendages in the insects. This loss rarely occurs on all the appendages; 



