FOOD OF INSECTS. 223 



can be either united into an air-tight canal, or be instantly separated, at the 

 pleasure of the insect. 1 



Another numerous race, the whole of the order Hemiptera, abstract the 

 juices of plants or of animals by means of an instrument of a construction 

 altogether different a hollow grooved beak, often jointed, and containing 

 four bristle-formed lancets, which at the same time that they pierce the 

 food, apply to each other so accurately as to form one air-tight tube, 

 through which the little animals suck up 2 their repast ; thus forming a 

 pump, which, more effective than ours, digs the well from which it draws 

 the fluid. 



A third description of insects, those of the order Diptera, comprising 

 the whole tribe of flies, have a sucker formed on the same general plan as 

 that last described, but of a much more complicated and varied structure. 

 It is in like manner composed of a grooved case and several included 

 lancets ; but the case, although horny, rigid, and beak-like in some, is in 

 others fleshy, flexible, and more resembling the proboscis of an elephant, and 

 terminates in two turgid liplets : and the accompanying lancets are them- 

 selves included in an upper hollow case, in connexion with which they 

 probably compose an air-tight tube for suction. The number and form of 

 these instruments are extremely various. In some genera (Musca) there 

 is but one, which resembles a sharp lancet. Others (Empis, Asilus} have 

 three, the two lateral ones needle-shaped, that in the middle like a scimitar ; 

 together forming so keen an apparatus, that De Geer has seen an Asilus 

 pierce with it the elytra of a lady-bird; and I have myself caught them 

 with not only an Elater and weevil, but even a Hister in their mouths. In 

 many horse-flies we find four ; two precisely resembling lancets, and two, 

 even to the very handles, buck-hafted carving knives. The blood-thirsty 

 gnat has five, some acutely lanced at the extremity, and others serrated on 

 one side. The flea, the spider, the scorpion, have all instruments for 

 taking their food of a construction altogether different. But it is impos- 

 sible here to attempt even a sketch of the variations in these organs which 

 take place in the apterous genera, and in many of the dipterous Iarva3. 

 Suffice it to say, that they all manifest the most consummate skill in their 

 adaptation to the purposes of the insects which are provided with them, 

 and which can often employ them not only as instruments for preparing 

 food, but as weapons of offence and defence, as tools in the building of 

 their nests, and even as feet. 



Some insects in their perfect state, though furnished with organs of 

 feeding, make no use of them, and consume no food whatever. Of this 

 description are the moth which proceeds from the silk-worm, and several 

 others of the same order ; the different species of gad-flies, and the Ephe- 

 merae insects whose history is so well known as to afford a moral or a 

 simile to those most ignorant of natural history All these live so short 

 a time in the perfect state as to need no food. Indeed it rnay be laid down 

 as a general rule, that almost all insects in this state eat nfuch less than 



1 For a full description of this instrument, see Eeaum. i. 125, &c. 



2 The mode, however, in which this is effected, in all insects furnished with a 

 proboscis, can scarcely be by suction, strictly so called, or the abstraction of air, since 

 the air-vessels of insects do not communicate with their mouths : it is more pro- 

 bably performed in part by capillary attraction: and, as Lamarck has suggested 

 (Syst. des Anim. sans Vertcbres, p. 193.), in part by a succession of undulations and 

 contractions of the sides of the organ. 



