410 



ARTHROPODA. 



and consists of a medial axis, 6, bearing on the inside six ' endites,' t', and 

 on the outer side two 'exites,' a flabellum or epipodite, a, and a gill, A. 



FIG. 411. Branchiopod appendages. 1 and II first and sixth legs of Branchipus grubei 

 (after Gerstacker); 111, fourth leg of Daphnia simus (after Glaus), a, flabellum; 

 7i, basis ; i, axon and its endites ; fe, gills. 



This becomes modified into the schizopodal form by a loss of the four 

 basal endites (those nearest 6) and the development of the two terminal 

 endites into exopodite and endopodite. Still the schizopodal condition is 

 so nearly universal among Crustacea that it must be accorded great weight 

 in classification. 



The appendages furnish a further diagnostic character in that 

 two pairs of antennae are present in the Crustacea (see, however, 

 Trilobitae). Antennae, it will be remembered, are preoral append- 

 ages innervated from the brain. In some cases, as many Ento- 

 mostraca, the second pair may lose their sensory functions and 

 become mere swimming organs. 



A carapace, recalling the mantle of the molluscs, is widely dis- 

 tributed in the Crustacea. It arises as a fold from the head, which 



