78 CRUSTACEA COPEPODA chap, hi 



hosts from salt to fresh water, or the reverse. America appears 

 to be the home of the Argulidae.^ 



The structure of an Argulid is exhibited in Fig. 48. In 

 front of the siphon, within which the styliform mandibles and 

 first maxillae work, there is a poison-spine (s^j) ; the appendages 

 which correspond to the second maxillae (mx) are modified into 

 sucking discs, but in the genus Dolops they terminate in normal 

 claws. The next pair of appendages, usually spoken of as maxilli- 

 pedes (mxp), are clasping organs, and behind follow four pairs of 

 thoracic swimming feet (1-4). The body is foliaceous, and they 

 always apply themselves to their hosts with the long axis pointing 

 forwards and parallel to that of the host, while on vaiious parts 

 of the under surface of the body are spines pointing backward 

 which prevent the parasite being brushed off by the passage of 

 the host through the water. These animals, alone among the 

 Copepoda, possess compound eyes. 



A short sketch has now been given of the variations in 

 Copepod organisation, but we cannot leave the subject without 

 pointing out the rich field which still remains for the 

 morphologist, especially in determining the true relationships 

 of the parasitic families. 



^ C. B. Wilson, Proc. U.S. Nat. Museum, xxv., 1902, p. 635. 



