288 ORDER DIPTERA 



They are perhaps of sHght economic importance as they do not 

 attack growing plants, but on accoimt of the great ease with 

 which they may be bred in captivity they have been the 

 basis of some most important investigations concerning the 

 transmission of hereditary characters. 



Another species is one that occurs as a pest in apples and 

 is known as the apple maggot (Rhagoletis pomo7iella), which 

 differs in its method of work from the codling moth larvae 

 in that the larvse work near the skin and make tunnels 

 through the apple. It punctures the skin and deposits eggs 

 inside. This goes on during the summer and the larvae 

 mature in autumn with the maturing of the fruit. They 

 hibernate as pupae. This species occurs now and then in 

 Ohio, but is not so universally common as the apple worm. 

 It is more distinctly a northern species, sometimes a serious 

 pest in New England and parts of the States and Canada 

 bordering on the Great Lakes. 



Family Hippoboscidse. — The family Ilijjpohoscidce includes 

 sheep ticks, and forest flies. They have the wing structure 

 of the Diptera, suctorial mouth parts, but a very remarkable 

 method of reproduction. Instead of extruding eggs, they are 

 retained in the oviducts and developed through the larval 

 stage, being nourished by nutritive fluids. They are not 

 extruded until they are ready to pass into the pupa stage. 

 They take no nutriment as pupae after leaving the oviducts. 

 There is no food taken until as adults. There is an adapta- 

 tion for the parasitic habit. This is a different sort of adapta- 

 tion than is found in any other group of Diptera except the 

 succeeding group. They are different from any other group 

 of animals. 



Sheep Tick (Mcloijluigiis uviniis, Linn.). — The sheep tick is 

 a common pest of sheep. It differs from the most of the 

 other members of the family in never possessing wings. The 

 head is small and sunken into the prothorax. The middle 

 portion of the prothorax is rather slender, contrasting with 

 the development of this region in the winged forms. 



It is of a reddish or gray-brown color, about one-fourth of 

 an inch long, and easily detected when present in any num- 



