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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



legs. Each appendage (C) is a hollow process of the body wall, dis- 

 tinctly jointed, and composed of six segments, of which the proximal 

 three are relatively thick, while the region of the distal three is slender 

 and rapidly tapering to the apex. 



Each appendage is supported on a lateral lobe of the body segment 

 (fig. 35 C, LB). The series of lobes appears at first glance to belong 

 to the dorsum of the abdomen, but each one, though so closely amal- 

 gamated with the tergum that the spiracle appears to be situated on 

 its dorsal part, really occupies a pleural position between the tergum 



Fig. 35. — Abdominal appendages of sialid larvae. 



A, larva of Sialis, showing jointed appendages of abdomen. B, metathoracic 

 leg of Sialis larva, with subcoxal sclerites at its base. C, abdominal appendage of 

 Sialis larva, showing division into basis (LB) and jointed stylus {Sty). D, 

 posterior end of larva of Chauliodcs, dorsal view, showing pygopods (Pp) of 

 terminal segment. E, the same, ventral view. 



and the sternum of its segment. The lumen of each lobe is separated 

 from the general body cavity by a vertical sheet of tergo-sternal 

 lateral muscles, and within the lobe arise anteriorly and posteriorly 

 muscles inserted on the base of the movable shaft of the appendage. 

 It is clear, therefore, that we have here an organ corresponding 

 in every respect with a gill-bearing appendage of an ephemerid larva 

 (fig. 34 B), and that in both of these structures the basal lobe repre- 

 sents the stylus-bearing plate of Machilis. and the movable distal 

 appendage the stylus. 



