APTERA. 



437 



would be unable to move a limb. Another characteristic, however, is required. They must 

 be always kept sufficiently open for the free passage of air, and it is not easy to see how these 

 qualities should be united, as a 

 flexible tube will mostly, if abruptly 

 bent, as is continually the case with 

 the air-tubes of the limbs, lose its 

 roundness at the angle, and shut 

 off the communication. An India- 

 rubber gas-tube is a familiar in- 

 stance of this property of flexible 

 tubes. 



The difficulty is, however, sur- 

 mounted by a simple and yet most 

 effectual plan. The tubes are double, 

 one within another, and in the in- 

 terspace a fine but very strong hair- 

 like thread is closely wound in a 



spiral. It will be seen that, by means of this structure, the tube can be bent in any direction 

 without losing its roundness. The long flexible tubes of Turkish pipes are made in a similar 



the basis, upon which is sewn the leather and silken outer 



CATTLE BOT-FLY.— nypoderma, or CEstrus bonis, a, Ply. b, Larva, c, Pupa, b and c, 

 As seen from the under side. (All magnified ; line at left-band side natural size of Fly.) 



manner, a spiral wire forming 



tube — one of the many instances where the 

 art of man lias been anticipated in the 

 animal creation. A third species (CEstrus 

 ovis), of which we give also an exact illus- 

 tration, is parasitic in the sheep, inhabiting 

 the frontal sinus, i. e., the open space be- 

 tween the bones on the forehead and between 

 the eyes. 



Hippoboscidpe, 



known under 



of Forest-flies, 



l short notice. 



The 

 popularly 



the name 

 deserve f 



These are round-bodied 

 insects with legs that can 

 cling with w o n d e r f u 1 

 force, and are capable of moving backwards, forwards, and sideways with 

 equal swiftness, so that they are not easily captured, even when they do horse, or forest-fly. 

 not take to wing. These insects are mostly found in or near forests, and 

 are very annoying to horses and cattle. As may be seen by reference to the 

 engraving, their integuments are covered with hair, and are remarkably tough and leathery. 

 The various species of Ticks belong to this family, and are closely allied to the Forest-fly. 



Although not included in Mr. Westwood's list of insects, the Lice are mostly considered 

 as belonging to this class, under the name of Apteka. There are very many species of these 

 obnoxious creatures infesting different animals and tribes, and at least three species are found 

 upon the human subject. 



SHEEP BOT-FLY.— CEstrus ovis. 

 from tbe under side 



a, Fly. b. Larva. c, Pupa, as seen 

 (Everything magnified.) 



Hippodosea equina. (Mag- 

 nified.) 



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