286 Insects and their Surroundings 



beetles may be found some species which have the 

 hind-wings fully developed and capable of flight ; 

 others with these wings so reduced that they can be 

 covered by the wing-cases without any folding ; 

 others again in which the wings have almost disap- 

 peared, though the wing-covers can be raised ; and, 

 lastly, others in which the two wing-cases are firmly 

 joined together by their inner edges so as to form a 

 single hard plate, organs originally wings thus being 

 transformed into an armoured covering for an insect 

 which has taken entirely to a terrestrial life. The 

 loss of wings by the female of the Common Cock- 

 roach was dwelt upon in the opening chapter (p. 29). 

 Cave-Insects. — Flying through the air, then, or 

 taking advantage of any resting or feeding place on 

 the earth and the plants which grow thereon, insects 

 have established themselves wherever animal life can 

 exist at all. And besides spreading themselves over 

 the earth's surface some insects have penetrated into 

 its depths. The caves which, especially in limestone 

 districts, extend in narrow galleries and vast halls for 

 miles underground are tenanted by many species of 

 insects belonging to several orders. Seven kinds 

 of Springtails are known to inhabit the cavern of 

 Mitchelstown in the south of Ireland, while dozens 

 of species of Springtails, Crickets and Beetles, have 

 been described from some of the caves of Carniola 

 in southern Austria and Kentucky in North America 

 (167, 168). Some of these are evidently recent im- 

 migrants into the underground world, being identical 

 with species commonly found in ordinary surround- 

 ings above-ground. Others, however, are true cave- 

 insects, evidently descended from ancestors which 

 strayed or were carried into the caves at some distant 

 period. They have now become specially modified 

 in the course of generations in correspondence with 



