186 SIMULIID.E. 



of legs. At the tail there is a similar sucker, formed in like 

 manner. No legs in their normal form are present. Williston 

 says the ultimate segment is furnished with several curved 

 appendages for attachment, so that probably various modifications 

 occur in the larvae of different species. 



The pupa is generally enclosed in a membranous cocoon which 

 is incomplete at the upper end, much resembling an empty egg- 

 shell with the top cut off. This is fastened to the stems of plants. 

 Audouin asserts that the larva spins an entire cocoon first and 

 then eats away the upper portion, the presumption being that the 

 water may reach the eight long filiform appendages (breathing 

 tubes) arranged in fan-shape form on each side of its upper end. 

 These appendages are arranged in pairs, and a similar structure 

 exists in the pupa of Chironomus. The perfect insect emerges 

 below the level of the water, and the process has been excellently 

 described by Verdat as far back as 1822.* It is also graphically 

 portrayed by Prof. Miall,f whose account is here reproduced. 



"During the latter part of the pupal stage, which lasts about a 

 fortnight in all, the pupal skin becomes inflated with air, which is 

 extracted from the water and passed, apparently, through the 

 spiracles of the fly, into the space immediately within the pupal 

 skin. The pupal skin thus becomes distended with air, and 

 ft&sumes a more rounded shape in consequence. At length it 

 eplits along the back in the way usual among insects, and there 

 emerges a small bubble of air which rises quickly to the surface 

 of the water and then bursts. "When the bubble bursts, out 

 comes the fly. It spreads its hairy legs and runs upon the surface 

 of the water to find some solid support up which it can climb. 

 As soon as its wings are dry it flies to the trees and bushes over- 

 hanging the stream." 



This author adds that some species winter as larvae and are 

 double-brooded, the first brood appearing in April and May, the 

 second in August. The eggs are laid in large numbers in a 

 gelatinous mass on the stems of water-plants and are yellow in 

 colour, with a thick shell, having some resemblance to the eggs 

 of Chironomus. 



Hagen speaks of the pupa-cases of a North-American species 

 (/S. pictipes, Hagen) being affixed in considerable numbers to the 

 rocks in swiftly running mountain streams and adds that they 

 resembled wasps' nests in appearance. 



Eecent investigations by Dr. Sambon in Italy have practically 

 established the connexion between the disease pellagra and some 

 species of Simulium. The outbreaks of the disease are said to 

 be confined to those districts infested by the fly, and to those 

 periods during which the insect is on the wing, the exact 

 times of appearance and disappearance of both the disease and 



* Naturw. anz. allg. Schw. Gesellsch. (1822). Translated by Osten Sacken 

 in the " American Entomologist," ii, p. 229. 



t ' The Natural History of Aquatic Insects," p. 185 (1895). 



