186 SIMULIIDiE. 



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

 Eianner. No legs in their normal form are present. AVilliston 

 says the ultimate segment is furnished with several curved 

 appendages for attachment, so that probably various modifications 

 occur in the larv£c 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 eiglit 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 Chironovms. The perfect insect emerges 

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

 described by Verdat as far back as 1 822.* It is also graphically 

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



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

 fortnight in all, IIh; |)upal skin becomes infiated \yitli aii-, which is 

 <>xtracted from the water and passed, apparently, tlirough the 

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

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

 assumes a more rounded shape in consequence. At length it 

 r,plits 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 th(^ bubble bursts, out 

 comes the fly. It spreads its hairy legs and runs ui)on 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 streai))." 



This author adds that some species winter as larva) 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 tiie eggs 

 of Chironomus. 



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

 (-S'.jp'iciipes, Hagen) being affixed in considerable nunibers to the 

 rocks in swiftly running mountaiji streams and adds that they 

 resembled wasi)s' nests in a])pearance. 



Recent investigations by Dr. tSambon in Italy have practically 

 established the connexion between the disease pelhigia 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 



* Natiirw. anz. allg. Sehw. Gesellsfb. (1822). Translated by Osteii Sacken 

 ill t]\(? "American Entomologist," ii, p. 229. 



t • The Natural History of Aquatic Insects," p. 186 (1895). 



