AMERICAN PARASITIC ARGULIDjE— WILSON. 



687 



The walls of the proboscis are formed of an upper and an under lip, 

 respectively, which are held in place and at the same time rendered 

 flexible b}^ a jointed chitin framework. 



The latter can be seen on either side of the proboscis tube as a series 

 of longitudinal ribs, forked at their distal ends, where they are united 

 to one another and to a transverse framework which bounds the oral 

 aperture and gives support to the mandibles and maxilhv. The pat- 

 tern of this framework, as well as the details of the mandibles and 

 maxillte, varies greatly in diiferent species, but the essential features 

 are the same in all, and 

 are as follows: 



The under lip forms the 

 posterior surface of the 

 tube and spreads down 

 over the hood-shaped end 

 and up a very little way 

 on the anterior side, ter- 

 minating in the shape of 

 a half-moon around the 

 lower border of the mouth 

 aperture (lig. IT). 



At either side this half - 

 moon is prolonged into a 

 triangular flap which pro- 

 jects upward over the 

 outer surface of the uppei- 

 lip, and must hence be re- 

 garded as a rudimentary 

 labial palp (/. p.). 



The remainder of the 

 ventral surface is formed 

 by the upper lip, which 

 terminates at the mouth 

 in a somewhat squarely 

 truncated {americanus, ca- 

 tostomi) or even emargi- 

 nate {n'igei\ megalops) lip proper, projecting into the concavity of the 

 under lip. 



In foliaceus^ in addition to the transverse opening at the end of the 

 proboscis, there is a narrow, somewhat lance-shaped longitudinal slit 

 extending along the anterior surface toward the base of the proboscis. 

 This slit is considerably longer than the transverse opening, and its 

 edges are sharply serrated where it merges into the latter. 



Hence the mouth opening has an elongated triangular form mfolia- 

 cem. But in catostovii the longitudinal slit is very much shorter than 



Fig. 17.— Mouth-pakts and chitin skeleton of proboscis 

 OF Argulus foliaceus (after claus). c, Chitin frame- 

 work; /., LOWER LIP; l. p., labial PALP; 7H. AND m'., LONGI- 

 TUDINAL AND transverse PORTIONS OF THE MOUTH OPENING; 



m d., mandible; ))!. v., maxilla. (Compare with Fig. S.) 



