OF INSECTS. 325 



kinds attached to the tail. Those of the chameleon 

 fly, the rat-tailed worm, and many of the common 

 gnats, exhibit beautiful examples of ingenious natural 

 mechanism. It is to the larvae of Diptera that we 

 apply the common term maggots or mawks ; some- 

 times also they are termed grubs, but that appellation 

 should be confined, for the sake of distinction, to the 

 larvae of the Coleoptera. They are often very, de- 

 structive to corn and meadow grasses by eating the 

 roots, and many of them, as is well known, rapidly 

 consume animal substances, both in a dead and living 

 state. The larvae of the flesh-flies, in particular, 

 (Sarcophaga, and certain species of Mtisca,) infest 

 living sheep, and frequently prove fatal to them. 



In the greater number of instances, the larva is 

 changed into a pupa without shedding the skin ; the 

 latter merely hardens, changes its form somewhat 

 by contracting, and thus becomes a case for the en- 

 closed insect. Sometimes, however, the skin is cast 

 off, and even a kind of cocoon formed ; and the nymph 

 occasionally retains the power of locomotion. This 

 takes place only with such kinds as are aquatic. 



This order is a most extensive one, indeed there 

 is every reason to believe that it falls very little short 

 of the Coleoptera in this respect, and, if we re- 

 gard the number of individual* belonging to many 

 of the species, they will be found greatly to exceed 

 all others. Clouds of musquitoes are common in 

 Northern Lapland, and in other countries, so dense 

 and extensive as to intercept the rays of the sun ; 

 and, when we consider the small size of these insects, 



