INSECTA. 



883 



were not prepared to meet with anything like 

 an approach to the same number in a perfect 

 insect. In the female of the Gryllotalpa 

 vutgaris we have found nine distinct segments 

 in the abdomen, besides the post-scutellum, 

 which resembles a tenth one in a rudimen- 

 tary condition on the dorsal surface between 

 the meta-thorax and base of the abdomen. In 

 the male of the same species there are also nine 

 distinct segments, but the penultimate and 

 ante-penultimate are in a rudimentary con- 

 dition, corresponding to those in the female 

 Forficula. The post-scutellum at the base of 

 the meta-thorax is as much developed as in 

 the female, and is very distinct as a portion 

 of the meta-thorax. \Ve have also found 

 the same number in a foreign species, Gryl- 

 lotalpu didact>/la. The similarity in the num- 

 ber of segments thus appears to connect the 

 Gryllutulpte with the Forjiculte. These va- 

 riations in perfect insects lead us to hesitate 

 in admitting thirteen to be the normal number 

 of segments, especially as we shall presently 

 endeavour to show that the head itself is com- 

 posed of more than one. The varied forms of 

 the body in the different classes are entirely 

 dependent upon the extent to which these 

 primary segments are developed, whatever be 

 their true number, and chiefly upon the greater 

 or less development of parts of the first four seg- 

 ments. But whether the changes in these seg- 

 ments be greater or less, they are always in 

 reference to the habits or economy of the indi- 

 dividual. Thus in the Coleoptera and Orthop- 

 tera the parts of the mouth are nearly equally 

 developed, and are admirably fitted for all the 

 purposes of manducation. In the Lepidoptera 

 some of these parts are developed to their 

 greatest possible extent, the consequence of 

 which is that the neighbouring parts become atro- 

 phied, and leave scarcely a trace of their former 

 existence. This is the case with the mandibles 

 and lips, the most conspicuous parts of the 

 mouth in the larvae of this order. In the imago 

 the maxillae are greatly elongated, and altered in 

 shape, to form a flexible tube, because the per- 

 fect insects are destined to take their food in a 

 liquid state, and because still further, the food 

 is produced in situations where it would be in- 

 accessible to the insect, were the mouth of the 

 same form as in those the food of which re- 

 quires to be comminuted by the jaws, before it 

 is passed into the stomach.* Then again in the 

 same segment in which the oral organs are 

 nearly equally developed, other parts are often 

 enlarged, and in like manner encroach upon 

 those which are in immediate connexion with 

 them. In the rapacious Neuroptera which 

 obtain their food solely by means of the organs 

 of vision, and are constantly hawking in search 

 of it in the brightest light, the corneae of the 

 eyes are expanded over nearly two-thirds of the 

 whole surface of the head, and in consequence 

 reduce to their minimum of development those 

 parts which are most conspicuous in the head 

 of Coleoptera, which usually obtain their food 



* See Newman on the External Anatomy of 

 lu sects, p. 13. 



by the aid of other senses. The causes which 

 regulate the development of the segments of the 

 thorax are exactly those which influence the 

 development of the head. In the mole-cricket, 

 which burrows in the earth for its food, the 

 second segment, or pro-thorax, with its ap- 

 pendages the anterior extremities, is enlarged 

 to its greatest extent, because it is necessary 

 that nearly the whole strength of the insect 

 should be concentrated in this segment, to 

 enable it to dig its way with ease and rapidity 

 through a resisting medium, while the third 

 and fourth segments, which bear the organs of 

 flight, in this species of minor importance, are 

 smaller than in most other insects. In the 

 Coleoptera, Geotrupid<E y which not only 

 burrow in the earth, but require to be trans- 

 ported from place to place in quest of food, 

 the pro-thoracic, and the wing-bearing meta- 

 thoracic segments are largely developed, and 

 form a great projxmion of the body, and the 

 intermediate segment, the meso-thoracic, en- 

 croached upon by both, is almost atrophied 

 between them. On the other hand, in the Hy- 

 menoptera, Lepidoptera, and Diptera, in which 

 the principal organs of locomotion are the 

 anterior wings, the meso-thoracic segment is 

 enormously enlarged, and the pro-thorax and 

 meta-thorax are reduced to a size of compara- 

 tive insignificance. 



These important modifications of structure, 

 by means of which every part of the body is 

 beautifully adapted to the habits and wants of 

 the individual, and the insect itself becomes an 

 agent employed by nature to work certain 

 necessary effects on other parts of Creation, are 

 accomplished during the metamorphoses by cer- 

 tain changes in the form of parts of the external 

 teguments. By this means many insects which in 

 their naked larva condition scarcely at all differ 

 in their general external appearance, are made 

 to assume forms, when they have undergone 

 their metamorphoses, so totally distinct from, 

 each other as to be instantly recognisable by the 

 most unpractised observer. The primary divi- 

 sion of the body into segments is effected simply 

 by a duplicature of the external covering. One 

 margin of the fold is carried over the other, and 

 a simple telescope articulation is produced. 

 In this way the body of the larva in its earliest 

 condition is first divided into its normal num- 

 ber of segments, and by a continuation of the 

 same process, as we have before shown, into 

 distinct regions. 



The articulations of the limbs and organs of 

 manducation are as much the result of changes 

 in the form of the external surface as the divi- 

 sion of the body into segments or regions. 

 The folding, the intussusception, the depression, 

 or the extension of certain portions of the inte- 

 gument, when solidified, at the completion of 

 the metamorphoses, serve all the offices, and 

 become parts of the different kinds of articula- 

 tions, which in principle are precisely similar 

 in insects to some of the more important ones in 

 the Vertebrata. In the simple approximation of 

 two surfaces, completely solidified, and allowing 

 of no motion between them, we discover the 

 common sutural connexion of some of the 

 3*2 



