SOME PARASITES OF SIMULIUM L \R\VE. 33 



shallowest. On closer examination the mass \vill be seen to 

 consist of numerous curiously shaped larvae standing upright 

 on the rock, to which the hind end of the abdomen is firmly 

 attached. These larva*, the largest known North American 

 species of which measure when mature -ome 12 mm., have the 

 following characters: The soft-skinned body is more or less 

 cylindrical, though the posterior thin! i- -omcwhat swollen. 

 The segments are poorly defined but the first three behind the 

 he.id. namely, the thoracic segment-, are usually distinctly 

 marked off from tin- following abdominal -eminent-. 



The prothoracic segment bear- a -inije leg (Plate I.. Fig. l) 



which i- apparently t\\ -\< >inted : tin- distal joint i- -mail and 



retractile and terminate- in a -inker which i- armed \\ith numer- 



on- hook-. \o other -e-meiit bear- any trace .f le^-, with the 



piion ol I'M- a|ical abdominal -e-ment when- the pair of anal 



prolei;- of -onir oilier lar\.e i- represente 1 by a powerful, armed 



di-k like -inker, by mean- of which the larva firmly attaches 



ii-'ll i" rocks or \e w .-iation \\hen at re-t. The -kin i- u-ually 



: vjveiii-li i^ray color in immature larva-, but gives place to a 



reddi-h bn>\\ n as t he\ inatn: 



The head i- -nb-c\ lindrical and i- n-uallv of a <larker color 

 than the re-t of the bod\ . It- chitinoii- inie-unieiit i- much 

 den-er and less ela-tic than that co\i-rin^ the remainder of the 

 boi|\. Tin- re-ult-. durii - >uth. in an e< d\ -i- of the heail 

 cap-ule alone, bein- n< \ more trei|in-ntl\ than that of the 



-r.il cntii iilar io\erin^ "1 the body. The lieu head cap-nle 

 e\po-ed alter -mil an e< d\ -i- i- |erfec!ly pi 14 men tie in Sininlimn 

 liirlifx-), llioii-h dark 5] "in form on it- \erte\ I'late I.. I 



2, a. i> and , . lolloucd b\ a -r.idn.il inlii-cation of the \\liole 

 -nrlace. Indixidiial- \\ere observed in which the almo-t black- 

 head c.tp-llle \\.i- half reillo\fd. e\po-ill<^ the new pi^melllle-- 

 cap-ule. entiivlv inde]iendeiiil\ of the bod\" cuticle, the ecdysis 



of \\hich \\a- never observed, except at pupation. 



( )n either -ide of the head are two black eye spots and on the 

 anterior border are two lateral tan-like organs borne mi elongated 

 pedicel-, which are u-e.l by the larva in procuring food. Th 

 fans con-i^t of numeroii- cur\ed rake- 'Plate I., 1 i-. 3) bearing 

 on one -ide Ion- -tiff" cilia which, when the fan is expanded, 



