410 



ARTHBOPODA. 



and consists of a medial axis, h, bearing on tlie inside six ' endites,' i, and 

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



Fio. 411.— Branchiopod appendages. 1 and fl first and slsth legs oi Branehipuagnitjci 

 (after Gerstacker); ii 7, fourth leg of Dap^iiiia .sinni.? (after Claus). n, flabellum; 

 ft, basis ; i, axon and its endites ; /f, gills. 



Tliis becomes modified into the sohizopodal 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 antenuje are present in the Crustacea (see, however. 

 Trilobitas). Antennas, it will be remembered, are preoral append- 

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

 mostraca, the second jiair 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 



