Localities in which Pellagra is Prevalent. 15 



two black specks, the posterior the larger and reniform, the 

 anterior elongate and nearly straight. 



From the first body segment following the head, on its 

 ventral side, arises a jointed leg extending forward and 

 turning upward beneath the head. Its extremity is armed 

 with rust-brown chitinous hooks by which it is enabled to 

 cling, the structure being an organ of locomotion. At the 

 posterior extremity of the body is a circle of microscopic 

 hooks for clinging, this larva like others attaching itself to 

 a web which it spins on the surface of rocks, and then 

 standing erect swaying about in the current. The external 

 respiratory organs consist of three tufts of soft white finger- 

 like processes thrust out above the posterior extremity of 

 the body, each lateral tuft consisting of four processes and 

 the median of about the same number. These structures 

 are retractile and are not visible on most of the specimens 

 collected. 



The colors of the larvae secured vary somewhat with age 

 and size, the very young being largely white, older ones 

 showing evident bands of black on the middle body seg- 

 ments. An example before me shows a black dot posterior 

 to the base of each fan-like brush of the head, while several 

 close-placed brown points are visible from above near the 

 posterior lateral margin, and a group of about six median 

 ones appears between them. Sutures of the head and pos- 

 terior margin black. Foot white, excepting the roughened 

 tip, which is rust-brown. Swollen posterior part of body 

 white beneath; ring of hooks brown. 



Fig. 2.— Pupae of S. venustum. A, adult emerging 

 From Straight Creel;, 1911. 



