354 NATURAL HISTORY. 



protruded more or less ; the lobes of the maxillae are generally fused together ; the mentum is small, 

 and the ligula usually furnished with side lobes (paraylossw). In the Bees, as already noticed (p. 286), 

 the ligula and maxillae are much elongated to foun the proboscis. 



The two pairs of membranous wings are attached to the upper part of the sides of the meso- and 

 metathorax, and above the base of each fore wing there is a small movable plate (tegnla), which is 

 regarded as forming part of the episternum. The surface of the wings is naked or furnished with 

 scattered hairs, and the membrane of which they are composed is usually more or less transparent, 

 although in some cases it may be dark-coloured. In certain forms belonging to the order the wings 

 are altogether absent, or they may be present in one sex and wanting in the other, or, as in the whole 

 tribe of Ants, there may be no wings in the workers (or infertile females), while the perfect males and 

 females possess them ; but where they exist the fore wings are almost invariably larger than the 

 posterior pair. All four wings are used in flight ; during repose they are generally laid together over 

 the back of the insect ; when in action the hind wings are held fast to the fore wings by means of a 

 row of minute hooklets placed along part of their front margin, which cling to a small groove at the 

 posterior edge of the front wings. This mode of union of the wings is characteristic of the 

 Hymenoptera ; and many years ago an entomologist maintained that this rather than the membranous 

 texture of the wings, which occurs in other orders of insects, had suggested to Linnaeus the name 

 given to the present order, the wings being, as he said, in a manner married to each other. 



The arrangement of the horny veins (see p. 283) which traverse and stiffen, these membranous 

 wings is also generally very characteristic. In some few instances they are reduced to a minimum, 

 but in most there run from the base of the fore wings certain longitudinal veins, at first nearly 

 straight, but afterwards more or less bent or waved, and then united by cross-veins in such a 

 manner as to enclose a few angular spaces on the disc of the wing. These spaces are known as cells, 

 and their number, arrangement, and forna furnish important characters for the classification and 



description of the Hymenoptera. In the fore wing (see figure) we find 

 along the front margin a strong marginal vein (costa), with another 

 longitudinal vein parallel and very close to it (the subcostal vein), and 

 the two unite beyond the middle of the front margin to form a horny 

 DIAGRAM OF HYMENoi'TERous WING, swelling (the stigmia). From this a small vein generally runs towards 



the extreme tip of the wing, cutting off a portion of the surface, which 



is called the radial cell, and may be divided into two or more by cross-veins. Another vein, which 

 runs along the middle of the wing from the base, and is continued in a more or less bent or 

 undulated fashion towards the apex of the wing, gives off a branch, which runs up to join the sub- 

 costal vein, and also gives off a branch, the space enclosed between which and the stigma and radial 

 vein is divided by a greater or less number of cross-veins into cells, called the submarginal cells. 

 Other cross-veins (known as recurrent veins) run back from these cells to the original main vein, 

 enclosing spaces known as discoidal cells. The veining of the hind wings is much more simple, and 

 of little or no systematic importance. 



The legs in the Hymenoptera possess great freedom of motion. They ai'e articulated to the 

 thoracic segments by very large, projecting, more or less conical hip-joints (coxca), to which the thighs 

 are attached by means of ring-like trochanters, which, in a great number of the species, are composed 

 of two joints. The tarsi are almost always of five joints, of which the first is generally considerably 

 longer than the rest, and often very different in form. 



The number of segments in the abdomen varies considerably, but not more than eight or nine 

 are recognisable, the remainder being either suppressed or concealed within the others. In some 

 forms the abdomen is attached to the thorax by the whole breadth of its base, but in the great 

 majority the first or first and second segments are contracted so as to form a slender stalk, by which 

 the union with the thorax is effected (see figure on p 355). According to some anatomists, the 

 hindmost part of the thoracic mass, which bears a pair of stigmata, does not really belong to the 

 thorax, but constitutes the first segment of the abdomen ; this, however, is a question upon which 

 we need not enter. The mode of union of the segments of the abdomen, and the relation of their 

 dorsal and ventral plates, has been already alluded to. 



The females of nearly all the species of this order possess organs, either projecting or protrusible 



