INSECT. 



851 



number of parts existing in all, although occasionally 

 rudimental or modified in various degrees, so as V 



Promuscis of Hemiptera (Pentatoma). 

 correspond with the functions which they have to 

 support. As, however, these modifications of struc- 

 ture are permanent throughout entire groups, serving, 

 in fact, for the establishment of orders, according to 

 some authors, it would surely be absurd to deny the 

 propriety of assigning to each variation a distinct 

 and fixed name. 



The mouth of the hexapod winged insects being 

 thus composed of a certain number of parts, may 

 much more easily be referred to one general type ot 

 form, than the mouths of the other annulose animals, 

 some of which have a much more complicated organi- 

 sation of the mouth than is to be found in insects ; 

 thus in the crabs we find not less than five pairs ot 

 jaws, whereas there are but two pairs of these organs 

 in insects. 



The parts of which the mouths of all insects is 

 composed, may be reduced to six; namely, four 

 lateral pieces disposed in pairs, and two other organs 

 opposed to each other, but in an opposite direction, 

 and which meet each other, so as to close the mouth 



The different parts of the mouth of a beetle (Blaps). 1 1, upper 

 lip ; m, mandibles ; m x, maxillae ; m p, maxillary palpi ; e 2, chin 

 or mentumj I 2, labium ; I p, labial palpi. 



from above and below ; the upper one being placed 

 above the upper pair of lateral organs, and the lower 

 one below the under pair of lateral organs. 



As regards the mode of taking their food, insects 

 have been divided by many authors into two groups ; 

 namely, those in which the mouth is furnished with 

 mandibles fit for biting, and those in which the mouth 



is suctorial. All the various modifications of form to 

 which we have above alluded may be referred to one 

 or the other of these sections ; and it is upon this cha- 

 racter that the leading division of insects into Man- 

 dibulata and Haustcllata has been adopted by various 

 authors ; although, since in one period of an insect's 

 life its mouth is fitted for biting, and in another for 

 sucking honey (as in butterflies), it may perhaps be 

 alleged that too great a weight has been assigned to 

 the structure of the mouth. The jaws ot biting 

 insects have a horizontal motion ; the mandibulated 

 insects must, of course, be characterised by the hori- 

 zontal motion of their jaws, and not as might, per- 

 haps, from the names of the two groups, be supposed, 

 upon the presence of mandibles in the Mandibulata, 

 or their absence in the Hamtellata ; because, as we 

 have already said, the mandibles or their represent- 

 atives are to be found in all insects. It would, indeed, 

 perhaps be advisable to propose other terms in lieu 

 of these, but as they are generally understood, we 

 shall continue to speak of the mandibulated and 

 haustellated insects, when we would distinguish them 

 by the biting or sucking mode in which they take 

 their food. 



Moreover, instead of treating of these two groups 

 separately, as has been generally done, it will perhaps 

 be more advantageous, as enabling us more readily to 

 show the modifications, which each organ undergoes, 

 to take the various organs seriatim prefacing their 

 description by the following general observations. 



In biting insects, or those which feed upon solid 

 matters, the four lateral pieces perform the office of 

 jaws, and move in a horizontal direction, the two 

 other pieces being regarded as lips ; the upper jaws 

 are more particularly denominated mandibles ; and 

 the lower jaws are named maxill<E, and, in general, 

 each of the latter is furnished with a slender jointed 

 appendage termed a palpus, which is never found 

 attached to the mandibles of winged insects ; in some 

 annulose insects the mandibles are, however, also 

 palpigerous. The maxillae are generally terminated 

 by two lobes, the outer one being very variable in 

 form. The upper lip is termed the labrum, and the 

 lower lip labium; but the latter is a much more 

 omplicated instrument than the former, and is fur- 

 nished, like the maxillce, with two short articulated 

 3alpi. 



In the sucking insects, the nutriment being essen- 

 :ially fluid, the necessity for biting jaws is obviated. 

 They are therefore either obsolete or they assume 

 the form of lancets, arid as such have a motion quite 

 different from that of the jaws of biting insects. The 

 mouth of these insects exhibits two distinct modifica- 

 :ions of form. In the first, the four lateral pieces, or 

 he mandibles and maxillae, are converted into slen- 

 der, setiform, or lancet-like pieces, forming a kind of 

 sucker, which is received into a membranous conical 

 or cylindrical and articulated gutter, as in the bugs ; 

 or are lodged within a thick, elbowed, and fleshy 

 heath, as in the flies. In the second modification, the 

 upper lip and the mandibles are either obsolete or but 

 lery minute : the lower lip is no longer a distinct and 

 oose organ, but is attached to the head, and is distin- 

 guished only by a pair of large palpi ; the maxillae, on 

 he contrary, are greatly elongated, but very much 

 attenuated, being transformed into two tubular threads, 

 .vhich, uniting at the edges, form a kind of sucker, 

 j-enerally rolled up in a spiral direction, and furnished 

 t the base with two minute palpi. We will now 

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