468 DIPTERA CHAP. 



of individuals, occur in various parts of the world ; one in New 

 Zealand is recorded as having been three-quarters of a mile long, 

 twenty feet high, and eighteen inches thick. There is good 

 reason for supposing that Mosquitoes may act as disseminators 

 of disease, but there is no certain evidence on the subject. The 

 minute Filar ia that occurs in great numbers in some patients, 

 is found in the human body only in the embryonic and adult 

 conditions. Maiison considers that the intermediate stages are 

 passed in the bodies of certain Mosquitoes. 1 



Fam. 5. Chironomidae (Gnats, Midges}. Small or minute 

 flies of slender form, with narrow wings, without projecting 

 rasft'i/ in, usually with densely feathered antennae in the male, and 

 long slender legs. The flies of this family bear a great general 

 resemblance to the Culicidae. They are much more numerous 

 in species, and it is not improbable that we have in this country 

 200 species of the genus Chironomiis alone. They occur in 

 enormous numbers, and frequently form dancing swarms in the 

 neighbourhood of the waters they live in. The species are 

 frequently extremely similar to one another, though distinguished 

 by good characters ; they are numerous about Cambridge. Many 

 of them have the habit of using the front legs as feelers rather 

 than as means of support or locomotion. This is the opposite of 

 what occurs in Culicidae, where many of the species have a habit 

 of holding up the hind legs as if they were feelers. The eggs of 

 Chironomiis are deposited as strings surrounded by mucus, and are 

 many of them so transparent that the development of the embryo 

 can be directly observed with the aid of the microscope. They are 

 said to possess a pair of air-sacs. The larvae, when born, are 

 aquatic in habits, and are destitute of trachea! system. They 

 subsequently differ greatly from the larvae of Culex, inasmuch as 

 the tracheal system that develops is quite closed, and in some 

 cases remains rudimentary. There is, however, much diversity 

 in the larvae and also in the pupae. The little Blood-worms, 

 \eiycommon in many stagnant and dirty waters, and used by 

 anglers as bait, are larvae of Chironomus. They are said to be 

 al 'E/iTTtSe? of Aristotle. The red colour of these larvae is due to 

 haemoglobin, a substance which lias the power of attracting and 

 storing oxygen, and giving it off to the tissues as they require 

 it. Such larvae are able to live in burrows they construct 



' Tr. Linn. Sue. Lond. (2) ii. LSS-1, p. 3t>". 



