INSECTA. 



IXSECTA. 



minuteness throughout the body, commencing from 

 r br.aU.ing warn, of which each segment normally 

 High MM of UMIB are frequently closed up, to that 

 i ill the put* of the system 



tot ma* elaborate rninu' 

 ta**ral Stigmata, or br. 

 ' i* pur. though 



.MrfW U greatly reduced. Between 



i U the froil communication ; and in iom part* of it, especially 

 fa liuinli of rapid flight, we find the ir-tube diUU-d into large air- 

 sac*, which both serve as reservoirs of air and contribute to dimiiiili 

 the tpedfio gravity of the body. By Uus extraordinary development 

 of thVrespiratory sytoni the apparent imperfection of the circulating 

 aDnanttts fa mnilisiaaseil linos th chief demand for a very rapid 



PI^M >**, *MMMarw^H' _ _r _ 



nOTvmeot of the 'blood in animals, which (like birds) put forth a vast 

 amount of muscular energy and activity, ariMi not to much oat of 

 the demand for nutrition a* from the necessity for a constant supply 

 of oxygen to the times, which in here provided for by the penetration 

 of the air iUelf into their substance. 



i . . 



i . . 



ttf. It, Xt 



Iff. JO, Karvou 



of the Common Cockchafer (Xtlolmtha 

 t a Caterpillar, or Larva. 



The nervous system in insects consists of a double nervous chord, 

 which is situated in the ventral portion of the body (being the reverse 

 in this respect to the vertebrate animals). This double chord is joined 

 at interval* by ganglia, which in larva correspond in number to the 

 joint* of the body, namely, thirteen. A* the larva is about to assume 

 the pupa state the abdominal ganglia gradually approach the thorax, 

 and eoneequently are nearer to each other, a circumstance owing to 

 the longitudinal contraction of the segment* at this time, at least 

 loch I* the ease in Lepidopterous larva. In the pupa state the 

 ganglia ire still more approximated, and the nervous chords are 

 curved aad distorted : the same number of ganglia however are 

 generally to he found ; but in the imago state of Coleopterous Insects 

 several of the ganglia have become confluent, so that the number is 

 eooaiderably reduced. In the Common Cockchafer (Mdolonlka r<d- 

 yarw), which may be taken a* an illustration of the general character 

 of the nervous system in insects, there is one large transverse ganglion 

 In the heed, consisting of two chief portion* joined laterally, and 

 which are expended on their outer aide to form the optic lobe. From 

 this large transverse ganglion the two nervous chords extend down- 

 wards and backwards, and form a ring which encircle* the (esophagus, 

 tannin which they are united by the second ganglion. These two 

 ganglia together lend off the nerve* which supply the various parts 

 of the head and its appvndagaa, the trophi, antenna, ftc. From 

 the lower part of the second ganglion the nervous chords are 

 uejliniiiil to the thorax, where we find three large ganglionic rnsasn*. 

 from which all the nerve* which supply the thorax and abdomen have 

 their origin. 



The development of the organ* of K-nne, and especially of the 

 visual apparatus, attains a high degree of development. The eyes 

 are here aggregated Into Urge compound misses, usually of nearly 



, which are so large as to occupy a considerable 

 part of the eidee of the bead. The structure of each individual eye 

 >whJeh U pearly of cylindrical form) win* most perfectly adapt* <1 to 

 brine; to a focus the rays which impinge u|>on it in the direction !' 

 Hi own axil, and by the mode in which the ningle eyes of each 

 aail,ihrhal maw are disposed, the range of vision is extended in 

 every direction, although the eyes themselves are perfectly motion- 

 Isea. This multiplication of cylindrical eyes precisely similar to each 

 other to gain an cud, which is answered in vertebrated animals by A 

 single globular eye, endowed with the power of motion on either 

 ride, ie fa remarkabU aocnrdanre with the general plan of structure, 



characteristic of the Articuiala, and is sometimes carried to a most 

 wonderful extent ; the number of siugle eyes in a common House- 

 Fly being 4000, in the llabbape-Butterfly 17,000, in the Dragon-Kly 

 24,000, and in the Mordella-Beetle 25,000. Besides the great com- 

 pound eyes moat insects have a few simple eyes disposed on the top 

 of their head, in the narrow space between the aggregate manes, 

 which appear to be of considerable use in directing their upward 

 flight There can be no doubt that insect* are possessed of the sense 

 of hearing, for though the precise organ which is subservient to it 

 has not been determined, there U ample evidence that they are guided 

 and influenced by sounds, one of the most striking instances of which 

 is that the male of some insects (such as Cicada, Crickets, Ac,), emit 

 peculiar sounds, which attract the females to them. These sounds 

 are produced entirely by mechanical means, and cannot be regarded 

 as vocal. It would seem probable, as has been hinted above, that 

 some part of the base of the antenna; is the auditory organ. There 

 is similar evidence that insects possess the sense of smell ; thus the 

 Flesh-Fly deposits its eggs in the thick fleshy petals of the Stapdia 

 (Carrion-Flower), deceived by its odour, which resembles tainted meat. 

 The sense of touch is very delicate in some insects ; such is the prin- 

 cipal purpose of the antenna;, and the feet in some cases are furnished 

 with peculiar organs, such as a soft cushion or a delicate expanded 

 sucker, that is adapted to receive tactile impressions from the substances 

 to which it is applied. 



The muscular system of insects is highly developed, being entirely 

 made up of the striated muscular fibre in its most perfect form, and 

 consisting not only of muscles for the contraction and elongation of 

 the trunk by the approximation or separation of its segments, but 

 also of numerous muscles which give motion to the legs and wings. 

 In insects of rapid and powerful flight these latter are so highly 

 developed as almost to fill the cavity of the thorax. The joints are 

 for the most part constructed so as to admit of but two kinds of 

 movement, namely, flexion and extension ; and the muscular apparatus 

 has consequently not that variety of action which is seen where the 

 ball and socket joint, which permits movements of circumduction, 

 takes the place of the simple hinge joint Nevertheless there are 

 no animals which surpass insects in command over the organs of 

 flight " Even the swallow cannot match the dragon-fly, which often 

 eludes its feathered pursuer as it can fly backwards and forwards, 

 right or left without turning. When we compare the space 

 traversed by an insect in a given time, with the dimensions of its 

 body, we find it vastly exceeds the similar ration in the bird, aud thug 

 we perceive that the locomotive powers of insects are far higher than 

 those of any animal whatever. 



" This power is most remarkably developed in the orders Neuroptera 

 (Dragon-Flies, Termites, ftc.), and Jlymenoptera (Bees, Ants, Ac,), and 

 it is remarkable that these are the very orders in which wo find the 

 most extraordinary manifestation of those instinctive tendencies, the 

 high development of which, with an almost complete absence of 

 intelligence, is a striking characteristic of the articulated series in 

 general, and of the class of insects in particular. 



" These tendencies may be considered as dependent upon an asso- 

 ciation between sensory impressions and muscular movement*, which 

 arise* from the original constitution of the nervous systems of these 

 animals ; and they may thus be regarded as necessities of their nature, 

 not in the least indicative of intelligence, design, or voluntary choice 

 on their own part*, but rather indicating the wise adaptation, by 

 which they have been constructed to work out plans of most admi- 

 rable elaborateness with the most wonderful perfection. Now these 

 and all other instinctive actions have for their object the maintenance 

 of animal life, as distinguished on the one hand from the mere 

 organic life of plants, and on the other from the mental or psychical 

 life of higher being*. Aud thus, if we consider the animal kingdom 

 as holding an intermediate position between the vegetable world on 

 the one side, and the domain of mind on the other, we should be 

 led to regard the cla*s of insects, and especially the orders Xeuroptcra 

 and Hymawptera, as its type." (Carpenter). 



Insect* are endowed with great powers of multiplication ; this is 

 accomplished with only one exception, by means of the sexual process 

 of generation. The exception referred to is that of the A phi* [Arms], 

 which is capable of propagation by a process that appears to be 

 analogous to that of gemmation amongst the lower animals. 



The egg* of insects are extremely variable in shape : the more 

 common form is oval ; they are however often round, sometimes cylin- 

 drical. Those of the common white butterfly are conical. In many 

 moths they are lenticular. The eggs of Uemerobiiu and several other 

 insect* are placed upon footstalks. 



The surface of the eggs i* generally smooth or nearly so, but it not 

 unfrequtiitly happens that they ore uneven, and display a great variety 

 of sculpture. 



White, yellow, and green are the predominant colours of the eggs 

 of insects : they are deposited in various situations, but always where, 

 the young larva; may find appropriate food when hatched. Thus we 

 often find them attached to the leaves or stems of plants. The 

 Ichnrumonidir deposit their eggs in or on the bodies of caterpillars, 

 and their larva; when hatched feed upon these animals. 



No insects come forth from the egg in their perfect condition, and 

 their state in many oases at the time of their being hatched is quite 



