65 



represent the curved lower sweep of the secondaries and tertials in the wings of birds, 

 Imlteres or balancers are supplied. In the Strepsiptera the lower-wings are largely 

 developed, and the fore-wings degenerate into balancers. • 



There is a departure from this third form, in which all the four wings are nearly of 

 equal length, and diverge considerably, 

 as in the Dragon flies, of which fig. 35 

 is an example, and Lace-winged flies. 



Where unusual projections are 

 met with in the fore-part of the body, 

 they are counter-balanced by a propor- 

 tionate extension or development of 

 the abdomen. The large head and 

 scythe-like mandibles of the Horned 

 corydalis are balanced by its dank and 

 elongated body. In a dried specimen 

 of this insect the want of symmetry, 

 occasioned by the contraction of the 

 abdomen, at once strikes the eye. The 

 antennae of the longicorn beetles are 

 thrown over the back in flight, and 



Fig. 35. 



the ovipositor of Pim'pla lunator streams behind. There are instances among the Hymen- 

 optera in which the abdomen is provided with a foot-stalk, and, in this arrangement, the 

 equilibrium of the insect is maintained without an inconvenient increase of weight. f 



Many beetles have what may be called the Tortoise-shape ; and it will be found that,, 

 as a rule, these are sluggish in disposition, falling, when disturbed, inertly to the ground. 

 They are, consequently, oftentimes in danger of being trodden under foot. But their 

 form is admirably adapted ^o resist pressure ; and an ox might tread one of them into the 

 yielding sod without doing it an injury. The potato-beetle is a familiar instance of 

 insects of this form, and so is the beautiful pie-bald beetle that frequents the silk-weed. 

 The water-beetles and bugs are admirably adapted to their environment. Belostoma 



grandis (fig. 36) is a wherry of the most approved form, 

 having powerful sweeps with which it can urge its way 

 through the water. It is also provided in its fore-legs with 

 grapnels, with which it can hold itself against the force of 

 the current. Insects of this form — and there are many of 

 them — may well be described as the Boat-shaped. 



We have already alluded to the fact that variations of 

 structure in winged insects are associated with diversities of 

 modes of flight. The ample-winged Attici have a flitting, 

 uncertain flight ; but the clean-cut, powerful wings of the 

 Sphinges (see fig. 37) are admirably suited both for hovering 

 over flowers and for making a sudden dash out of the way of 

 harm. Insects that have wings of an intermediate size are 

 those that have the most stately flight. Danais Archij^pits, 

 for instance (fig. 38), sails through the air with a grace and 

 dignity that are perfectly charming. And this creature, too, 

 is capable of long-sustained efibrt. It is known to be migra- 

 tory, and to pass in flocks from one district to another. 



In the calm summer and autumn evenings how amusing 

 it is to witness the sportive dances, in the beams of the falling 

 sun, of Ephemera and Tipulse. The long limbs of these insects 

 retard a forward movement, but yield readily to an upward 

 flight. The mere weight, however, of the appendages soon 

 brings the creatures down when the force of the wing-stroke is abated. Renewed efibrts, 

 again and again, give an upward movement, and so the mazes of the airy dance are- 

 threaded. 



Fig. 36. 



