284 



NATURAL HISTORY. 



AND SIDE VIEW (K). 



a, Antennae ; &, eyes ; c.Ocelli ; d, Clypeus, which in the Front View conceals 



the Labrura 



this is usually of a blackish or brownish tint, the wing-veins become plainly marked. The mode of ram- 

 fication of these veins is exceedingly characteristic of different groups of insects, and consequently 

 of great importance in their classification. In some cases the deposition of horny material in the 

 wing is not confined to the veins, but extends throughout the wing, which then becomes a horny 

 or leathery organ, unfitted to assist in flight. This change usually takes places in the fore wings 



alone, which then serve as protective cover- 

 b ings to the greatly developed and move 

 delicate posterior wings, the true organs of 

 flight, which in repose are folded up and 

 packed away on the back of the abdomen 

 beneath the firmer anterior pair. In the 

 Beetles (see Fig. 1), which furnish the best 

 examples of this modification, the horny fore 

 wings, called elytra, when closed, meet in a 

 straight line down the middle of the back, 

 usually concealing the whole dorsal surface 

 of the body, except the first segment of the 

 thorax (prcnotuni) and a small, shield- shaped 

 Fig. 4.-HEAD OF HORNET ( Vespa crabro} ENLARGED, FROXT (A) piece of the mesO notum (the scutettum) ; in 



other insects which possess horny or leathery 

 fore wings, these generally overlap towards 

 the end ; and in the Bugs only the first portion of the wing becomes horny, and the overlapping 

 terminal parts are membranous. Such fore wings are called tegmina and hemelytra. 



Exceptionally many insects belonging to the most various groups, are always wingless, or 

 the males are winged and the females apterous ; and besides these certain entire groups, especially 

 of parasitic insects, contain none but apterous species. Either of the pairs of wings may become 

 greatly reduced in size, and apparently useless, while the other pair is fully formed ; and in 

 one whole order the fore wings ^ _ 



\ v\ ^^~ ^i ' ' 



hind wings are represented by 



a pair of small organs, consist- 

 ing of a slender stalk, termi- 

 nated by a little knob, which 

 have received the name of 

 halteres or balancers. 



The head, or the foremost 

 of the three divisions of the 

 body (Fig. 1), when examined 

 as a whole, appears to be a A 

 solid horny case, but a con- 

 sideration of its appendages 

 leads to the conclusion that it 

 is composed of several segments. 

 On the upper surface or at the sides it bears a pair of jointed organs called antennae (Fig. 4, ), 

 and a pair of eyes (6), which are almost always of the kind called compound ; beneath it shows the 

 organs of the mouth, which are subject to the most remarkable modifications. 



The apparently homogeneous case of the head is considered to be divisible for descriptive 

 purposes into various regions ; thus the space between the eyes is called the forehead, in front of 

 which is a part known as the clypeus (d), and the two together form the face. The crown of the 

 head is called the vertex. Immediately in front of or beneath the clypeus, closing the mouth 

 in front, is a small plate, usually movably articulated, and called the upper lip or labriim. On 

 the vertex there are in many insects two or three simple eyes, or ocelli (c). the general structure of 

 which and of the larger compound eyes will be explained farther on. 



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Fig. 5. VARIOUS FORMS OF ANTENNA. 



A, Locusta; B, Apia; c, Silpha; D, Nt-orophorua ; F, Volucella; v, Elater ; o, Ctenocerus; 

 H, Mololoniha , I, Aga'us. 



