154 



BRANCH ARTHROPODA 



The Wings. — As the ordinal name indicates, these insects 

 have two membranous wings. No fly has more than two 

 wings and only a few are wingless. They have, however, 

 vestiges of a second pair, called halte'res or balancers, ending in 

 short knobs. They are used in directing the flight and are be- 

 lieved by some to be auditory organs. 



Family Mus'cidae. — The common house-fly (Mus'ca domes' lica) is too well 

 known for our comfort. It hibernates. One will recall having seen flies 

 about the house during the winter. They breed about stables in the sum- 



Fig. 124. — Typhoid fever or house-fly {Mus'ca domes' lica): a, Adult male; 

 b, proboscis and palpus of same; c, terminal joints of antennae; d, head of 

 female; e, puparium; /, anterior spiracle; all enlarged. (Howard and 

 Marlatt, Bull. U. S. Dept. of Agriculture, 1896.) 



mer. The eggs, numbering about one hundred, hatch in about twenty- 

 four hours. The soft, white, cylindric, footless larva is called a maggot. 

 It feeds and grows for about a week, molting twice, and then pupates 

 within the larval skin, or -pupariuvi, for another week. It then makes a 

 circular opening in the puparium and emerges as the adult fly, thus giving 

 time for a numlaer of generations. In a summer the offspring of a single 

 fly may reach incredible numbers. It is now known that the principal in- 

 sect agent in the spread of typhoid fever is the common house-fly, and 

 great care should be taken to prevent its breeding. All human and horse 

 excreta should be kept in fly-tight vaults and sprinkled with chlorid of 

 lime or quick lime at least once a week, unless wanted for fertilizing 

 purposes. All garbage cans and swill pails should be kept covered, and 



