122 Objects for the 



thorax, and it rises with its head upwards to breathe 

 through them. As soon as the last change is at hand, the 

 pupa raises its thorax out of the water entirely, and 

 slightly turns up its tail, floating like a boat ; presently 

 the skin bursts, and the head of the enclosed perfect 

 insect emerges, the long antennae wave to and fro, and the 

 frail bark rocks from side to side in some peril, for the 

 lightest breath of air would overset it. Then one by one 

 the legs are drawn forth and stretched forward to some 

 floating leaf or stick whereby to steady itself ; slowly the 

 rest of the body follows ; the wings, hitherto pressed to 

 its side, crumpled and damp, are dried by the warm atmo- 

 sphere, and the quick breathing of the little Gnat sends a 

 rush of air through the delicate veins ; they are gently 

 waved for a few seconds, then up and away flies the 

 rejoicing creature into its new and happy life. 



Such is the history of the pretty microscopic object on 

 the slide before us. 



Of its structure it is necessary to know that all the 

 Diptera are distinguished from other orders of insects by 

 having only two wings, and a pair of stout organs, called 

 halteres, which are supposed to represent the posterior 

 wings of the four- winged tribes, and respecting which ento- 

 mologists are much divided. They have been specially 

 noticed at page 142. The Diptera have mouths variously 

 constructed for their necessities. Their food is essentially 

 fluid ; the juices of plants or of insect bodies, and of 

 decomposing matter, forming their nourishment ; and, 

 therefore, instead of the strong horny mandibles of a 

 Beetle, we find in such flies as Tabanus a pair of lancet- 

 like organs for plunging into the skin of the animal whose 

 blood it delights in, and beneath these another pair, to 

 which are attached large palpi, exactly corresponding to 

 the maxillas and maxillary palpi of the Coleoptera; a 

 labium or lower lip, which in all flower-haunting and 

 honey-loving flies is very long and beautiful, as in Rhingia, 

 Syrphus, Conops, and many of the Muscidse ; a labrum or 

 horny borer prolonged in the predaceous flies, and very 

 remarkable in the Empidse and Asilidse, which have also 



