210 



KNOWLEDGE 



[September 1, 1890. 



alone be sufficient to excite repugnance and to prevent its 

 habits from being much studied. But as this smell com- 

 pletely goes off after death, there is nothing but the 

 natural prejudice against a personal parasite, and one so 

 closely associated with uncleanly conditions, to render a 

 careful examination of the dead insect an unpleasant 

 experience. There are many delicate touches in the 

 portraiture even of an insect which, when alive, is so 

 repulsive ; it is not all coarseness and vulgarity, and the 

 compound microscope, the use of which is necessary to 

 make out the minuter details, reveals many interesting 

 featm'es. 



For examination the insects may be killed by being 

 plunged into hoitimj water, or by being exposed for a time 

 to the fumes of chopped laurel leaves. In either case, 



their sickening 

 smell soon disap- 

 pears. Even at 

 their largest, they 

 are not more 

 than a quarter of 

 an inch long, and 

 hence are too 

 small and deli- 

 cate to be touched 

 with the fingers 

 without great 

 risk of damage, 

 and a pair of fine 

 forceps is neces- 

 sary for handUng 

 them. When 

 fully grown they 

 are of a deep 

 rust-red, tinged 

 with black here 

 and there in the 

 abdomen. The head and fore-parts are somewhat lighter 

 than the rest of the insect. Of the three dixisions of 

 the body, the head (Fig. 2) is the smallest ; its hinder 

 part is of an oblong shape, broader than long. The 

 eyes form projecting knobs at the sides, and the base 

 of the mouth organs a considerable prominence in front, 

 whereby the head, as a whole, acquires roughly a pen- 

 tagonal outline. 



The mouth organs form a sort of beak, called the rostrum, 

 and tills, as is iisually the 

 case in the Hemiptera, is 

 tucked back underneath the 

 head (Fig. 3), running along 

 the central line as far as the 

 base of the first pair of legs, 

 the head being slightly 

 grooved beneath for its ac- 

 commodation. At its j unction 

 with the head, the rostrum is 

 more flexible than elsewhere, so that it can be brought out 

 from the position of rest and held either pointing vertically 

 downwards, or even sloping forwards, when required to be 

 used. By reason of the constant i^resence of such a beak-like 

 apparatus as this, the name Ehynehota, i.e. beaked insects, 

 is frequently used instead of Hemiptera as the name of the 

 order. Lapping over the front of the beak, at the spot 

 where it joins the head, is a triangular plate, the labrum, 

 or upper lip (Fig. 2, /). The beak itself (Fig. 2, /•) con- 

 sists of a three-jointed, tubular, or rather gutter-shaped 

 organ — the labium — the channel of which is closed above 

 {i.e. on the surface which is forward-looking when it is in 

 use) by a thin transparent membrane, which is easily 



Fig. 2. — Head of Bed-Bug. «ith Rostkum 

 EXTENDED, a, antennae; c, crown; e, eyes; 

 /, labrum ; r. rostrum. 

 N. B. — The last joint of the antenna and 



part of the next have been removed. 



Fig. o. — Side View of Head 

 OF Bed-Bug, showing position 

 of rostrum (r) in rest. 



rujitured. Within the channel lie, side by side, and per- 

 fectly free, four fine, straight, bristle-like organs, which 

 represent the mandibles and maxilhe of other insects. The 

 mouth is therefore of the suctorial type, and suited only 

 for feeding upon liquids ; but it is adapted, not solely for 

 sucldng up exposed juices, as is that of butterflies and 

 moths, nor for licking them up like that of bees, but for 

 getting at liquids which are enclosed within covers or 

 boundaries which need to be pierced before their contents 

 can be reached. There is thus no power of biting, strictly 

 so called ; hence the term "bug-bite," like " flea-bite," is 

 somewhat inexact. 



In the presence of this boring apparatus, the whole 

 order of bugs agrees with many of the flies, notably with 

 gnats and mosquitoes, whose piercing bristles create so 

 much pain by the minuteness of the punctures they make 

 in our skin. Notwithstanding the general agreement, 

 however, there is one strongly marked difierence between 

 the two orders ; flies always have one pair of palpi and 

 sometimes two, attached respectively to the maxilhe and 

 the labium, but no such organs are ever found in bugs ; 

 hence the mouth in the Hemiptera is of a simpler con- 

 struction than in the Diptera, through the suppression of 

 parts which are, except in this order, almost universally 

 present, and generally very prominent. This suppression 

 and simplification is the more remarliable 

 because the bugs are in some respects a 

 more primitive race of insects than the 

 flies, and might so far have been expected 

 to show a more generahsed type of mouth. 

 It is impossible at present to do more 

 than speculate as to the significance of 

 this absence, as separate organs, of parts 

 which are in most insects amongst the 

 most prominent of the food-taking appa- 

 ratus, and which are endowed with such 

 a power of persistence, so to speak, that 

 in some cases they remain distinct after 

 the organs to which they belong, and of 

 which they are appendages, have become 

 fused with the rest, or have disappeared 

 altogether. Too Uttle is yet kno^vn of the 

 function or functions of palpi in general, to 

 be able to imagine what can be the influence upon the 

 economy of the insects of the defect under which they 

 labour. One would think that by contrasting the habits 

 of the not-palpi-possessing Hemiptera \vith those of the 

 palpi - possessing Diptera, it would become possible, 

 by detecting constant difterences between the two orders, 

 to arrive at some valid conclusion as to the function of 

 these organs. Such, however, does not seem to be the 

 case, and if there is any marked difference in the way 

 of taking the food, or in other respects, it has yet to be 

 discovered ; we know no more why the blood-sucking 

 mosquito should possess palpi, than why the equaUy 

 ' blood-sucking bug should be without them. Some main- 

 tain, however, that the channel-like beak itself consists 

 of the fused labial jsalpi instead of the pair of jaws to 

 which they belong, in which case the above remarks 

 would lose some of their force. 



Of the two pairs of bristles (Fig. 4) one (the mandibles) 

 is considerably stouter than the other (the maxilla-), and 

 the latter are exceedingly fine and delicately saw-like at 

 the free end. ' Each mandible possesses a sort of flange, 

 along which the corresponding maxilla slides, and thus the 

 four bristles unite into one boring weapon. As everyone 

 knows, the wound this weapon can inflict is, at least in some 

 cases, exceedingly painful and productive of consider- 

 able inflammation. Not that any poison is instilled 



Fig. 4. — Pierc- 

 ing ArPAKATlS 



OF Bed-Bog. 



md, mandibles ; 

 mx, maxilhe. 



