MUSCULAR SYSTEM. 



530 



articulated appendages, the legs and wings, 

 must undergo a still further improvement, and 

 the means whereby this is accomplished are 

 sufficiently manifest. The nervous ganglia are 

 accumulated into a few large and powerful 

 centres of innervation ; the rings of the body, 

 to which the locomotive organs are attached, 

 are dilated and strengthened in proportion to 

 the force of the muscles placed within, and 

 constitute three thoracic rings of such firmness 

 and inflexibility that they may well be looked 

 upon as forming a distinct division of the exo- 

 skeleton, and give rise to the distinction laid 

 down by entomologists betweeen the head, the 

 thoracic, and the abdominal segments that enter 

 into the composition of an insect's body. But 

 the same concentration of the nervous system, 

 which permits an Insect to possess the extraor- 

 dinary powers of flight with which it is gifted, 

 allows by the increased perfection given to 

 the brain, the possession of elaborately con- 

 structed senses. The eyes assume a complexity 

 of structure that is truly wonderful, the sense 

 of touch attains extreme delicacy, and indubita- 

 bly the means of smelling, of tasting, and of 

 hearing are now conferred, however incapable 

 we may be of pointing out the mode in which 

 they are exercised ; nay, it is extremely proba- 

 ble that capabilities of perception of which we 

 can form no idea, are bestowed upon the Insect 

 races commensurate with the activity of their 

 movements and the wide range of duties they 

 are appointed to perform. 



During the metamorphosis to which Insects 

 are subject, that is to say during the advance- 

 ment of these creatures from an embryo condi- 

 tion to their mature or perfect state, changes 

 are constantly in progress, both in the nature 

 and arrangement ot the locomotive organs, and 

 of course as these changes are effected, the 

 entire disposition and even the vital properties 

 of the muscular system appropriated to their 

 movements undergo a considerable modification. 

 The larvae of many genera have externally the 

 appearance of the simplest worm, being pro- 

 vided with not even any vestiges of the loco- 

 motive apparatus that subsequently is to be 

 developed : even the rings or segments of the 

 body are entirely soft, the cuticular covering 

 being of extreme tenuity, and the tegumentary 

 muscles, as a natural consequence, propor- 

 tionally rudimentary in their structure. In 

 such larvae the nervous system exhibits the 

 lowest condition found among theapodous An- 

 nelidans, and the eyes and external senses are, 

 if they exist at all, of the humblest possible 

 character. This is the case, for example, in 

 the maggots of many Dipterous and Hymenop- 

 terous Insects. 



In others, as for instance in the caterpillars 

 of the Lepidoptera, the locomotive powers are 

 of a slightly ameliorated description : the larva 

 possesses a distinct head, and to the succeeding 

 segments, rudely constructed limbs named legs, 

 and others bearing still less resemblance to the 

 locomotive members of the future insect, to 

 which the name of pro-legs has been appro- 

 priated, are the only instruments of progression . 

 Even in the most perfect larvae, as in those of 



the aquatic Beetles, the form is elongated and 

 resembles that of an Annelidan ; the legs are 

 comparatively feeble and of small size, and 

 simple ocelli replace the compound eyes that 

 afterwards become developed in the perfect 

 Insect. 



During the progress of the metamorphosis, 

 the nervous system within is undergoing a pro- 

 cess of concentration precisely comparable to 

 that which has been noticed in advancing from 

 the lower to the higher classes of ARTICULATA. 

 The ganglia coalesce and become less numerous, 

 the encephalic pair attain a higher development, 

 and as this is accomplished the legs and wings 

 of the mature being sprout from the sides of 

 the segments appropriated to sustain them, 

 enclosed in and defended by cases of cuticle 

 temporarily provided, which constitute the 

 covering of the pupa or chrysalis, until at 

 length, the aggregation of the previously sepa- 

 rated ganglia being completed and the brain 

 perfected to the extent required, the pupa-case 

 is thrown off, the newly-formed limbs expand, 

 and the insect, with its newly-acquired limbs, pos- 

 sesses an additional system of muscles, which 

 have been developed with their growth, and 

 only arrive at their full state of perfection when 

 the body has ceased to grow, and the genera- 

 tive system, having attained its complete pro- 

 portions, proclaims the animal mature and able 

 to propagate its species. 



The addition of wings, indeed, to the body 

 of flying insects would seem to be a provision 

 specially connected with the distribution of the 

 progeny to which they are to give birth, and all 

 the phenomena connected with their develop- 

 ment and that of the muscular apparatus pro- 

 vided for their movements to have relation to 

 this great and closing act of the insect's exist- 

 ence. The period of time during which these 

 animals live in their imperfect or wingless state, 

 during which many of them have important 

 offices assigned to them, constitutes, in most 

 cases, by far the longest portion of their lives, 

 and some aquatic larvae, indeed, reside for 

 months or even years in the water under their 

 immature or wingless form, which perish in a 

 few hours after they have been gifted with the 

 means of aerial locomotion. Had they never 

 been furnished with wings, it is abundantly 

 evident that the species of such insects could 

 never have been dispersed beyond the precincts 

 of the pond or the ditch in which the parent 

 had passed her existence, but the brief space 

 allowed them to enjoy life in the winged con- 

 dition is sufficient for the achievement of the 

 great object in view, and the Eplieweron and 

 the little Gnat, while they appear to be only 

 sporting out their evening's life amid the sun- 

 beams, are, in fact, disseminating their offspring 

 through different localities. 



The next class of HOMOGANGLIATE animals 

 comprises the ARACHNIDANS, the Scorpions 

 and the Spiders, animals visibly intended 

 to be destroyers, appointed to keep within 

 due limits the different races of the Insect 

 world, and by assisting in the great work 

 of destruction that is on all sides in progress 

 against them, to prevent their fertility from 



