emery: simulium vittatum in Kansas. 333 



thorax there appears on the full-grown larva black spots which 

 are the pupal gills, folded and drawn up beneath the skin. 



At the caudal end is a sucker-like aperture used to hold the 

 larvse to the stones and debris in the ripples. It is made up of 

 a series of rows of tiny hooks. On the dorsal side the sucker- 

 like organ is produced into a V-shape. (PI. XLI, fig. 35a.) 

 Cephalad of this are the breathing gills. In vittatum these 

 are three-branched, as membranous sacs, finger-like, when 

 the larva is undisturbed in the water. 



In preserved specimens the gills can not be seen unless forced 

 to distend by pressure from a dissecting needle placed cephalad 

 of them. 



The larvae intermediate in size appear to seek the swifter 

 ripples, while those about ready to pupate and the smaller ones 

 seek the less violently agitated parts of the ripples. When 

 moving about on the stones they have a looping motion, similar 

 to that of a geometrid larva. They more frequently make 

 their looping motion laterally instead of dorsally. In doing 

 this they first attach their thoracic leg, then draw their caudal 

 sucker forward and attach it. Frequently one can see the silken 

 thread they spin as they move about. It looks as though they 

 always kept the thread attached, because at any time they are 

 washed from the stones or debris they will float away from one 

 to ten inches, holding fast to the thread, which they spin as 

 they go. 



The larva possesses two silk glands, laterally placed, ex- 

 tending about three-fourths the length of the body, then re- 

 curved, U-shaped, extending back to the thoracic segments. 

 The outlets are the two ducts which lead into the hypo- 

 pharynx.- Besides being used as a means of security, the 

 thread is used to float out in the ripple while feeding, and for 

 building the pupa case. Ordinarily, while feeding, the larvse 

 attach their caudal sucker to the object in the ripple and let 

 the rest of their body and head float at an angle of sixty to 

 ninety degrees. I have watched them in the water draw their 

 fans in and scrape them with their mandibles as though col- 

 lecting food. 



With the kind assistance of Dr. Grace M. Charles, of Kansas 

 University, we found several species of diatoms and the fol- 

 lowing kinds of algse in the digestive tract, which I take to be 

 the food of S. vittatum: Conferva, Scendesmus, Chlanydomo- 



2. N. Y. St. Mus. Bui. 68. 



