AX ATOMY OF INSECTS. 237 



In the Butterflies and Moths the change is apparently greater than in the Bees, although when 

 the structure of the mouth in. these insects is investigated the different parts are, if anything, more 

 distinct. In Butterflies and Moths the upper lip and mandibles form three little plates, placed 

 on the front of the head between the large eyes, but entirely concealed beneath the dense clothing of 

 hairs with which that part is covered. Springing from the front of the head, beneath these rudi- 

 mentary parts, we find a tapering organ, which is rolled up into a close spiral when in repose, but can 

 be stretched out generally to a great length, and possesses considerable mobility. It is by means of 

 this organ that the insects are enabled to suck up their food, which consists for the most part of the 

 sweet juices of flowers ; and, on investigation, it is found to consist of the maxillae, which are produced 

 into two thread-like organs, each bearing on its inner surface a half-tube, the junction of the latter 

 forming the tubular organ through which the nectar passes. At their base these elongated maxillae bear 

 small palpi. The lower lip (or labium), like the labrum, is considerably reduced in size, and, indeed, 

 may be nearly rudimentary ; but, notwithstanding this reduction, it bears a pair of very large, usually 

 three-jointed, palpi, which are in mcst cases densely clothed with hairs, and constitute those organs 

 which may be easily observed in. many Butterflies, projecting like a pair of stout horns in front of 

 the head, and between which the spiral proboscis is rolled up when at rest. 



In the other two principal types of haustellate, or sucking insects, all the parts of the mouth 

 take part in the formation of the sucking organ, and in both the labium is convei'ted into a sheath, 

 within which are contained the representatives of the mandibles and maxillae, reduced to a bristle- 

 like condition. One great order of insects, distinguished at the first glance by the presence of only 

 a single pair of perfect wings, the hind wings being represented by the little knobbed organs already 

 described as halteres, is further characterised by having the labium converted into a sucker, often of 

 a more or less fleshy texture, the upper cleft of which is closed by the elongated labrum, and within 

 the tube thus formed are some bristle- or lancet-like organs, representing the mandibles and maxillae, 

 frequently accompanied by an unpaired piece of the same kind, which appears to spring from the 

 labrum, and is called the epipharynx. The number of bristles or lancets contained in this sucking 

 mouth may vary not only in different families or species, but even in the two sexes of the same 

 species. The full number of five is scarcely found except in the females of blood-sucking species 

 (such as Gnats and Breeze-flies) : in the males of these and in most other forms there are only three 

 bristles, two of which are proved to represent the maxillae by the attachment to them of palpi near 

 their base. It is then a matter of uncertainty whether the third bristle is to be regarded as the 

 epipharynx, the mandibles being altogether wanting, or as composed of the two mandibular bristles, 

 united into one. The extremity of the proboscis in this type is frequently enlarged into a double 

 pad, like a pair of lips, one on each side of the aperture. This has been regarded by many anatomists 

 as representing the labial palpi, by others as formed by the ligula and labial palpi united. It is well 

 seen in the common House-fly and in the Bluebottle. The function of the bristle-like organs in the 

 interior of the proboscis is to pierce the tissues containing the blood or vegetable juices upon which 

 these insects feed. 



The Bugs and their allies have another form of sucking mouths, to which the name of rostrum is 

 given. As already stated, its sheath also consists of the metamorphosed labium ; but here it forms a 

 longer or shorter beak, tapering to a point and divided into three or four distinct joints, which may 

 very well represent the joints of the labial palpi united along the middle line. The jointed organ 

 thus produced, which is articulated to the lower surface, or the apex, of the head, has its sides bent 

 round in such a manner that their edges come into close contact, or may be united together, forming 

 a closed tube, except towards the base, where the edges of the first and sometimes of the second joint 

 remain at some distance apart. The little gap thus produced is, however, closed by the more or less 

 elongated labrum, which thus again completes the sucking-tube. Within this tube we find four long 

 and fine bristles, representing the mandibles and maxillae, and these, as in the Flies which were last 

 described, can be pushed forth and retracted by the action of muscles attached to their bases. They 

 serve, as, indeed, in one case is pretty well known, to pierce animal and vegetable tissues, and thus 

 enable the juices contained in them to be readily sucked up. The maxillae in these insects are quite 

 destitute of palpi. 



Hitherto we have been considering the characters presented by the mature or adult insect ; but 



