34 



THE POPULAR EDUCATOR. 



though all that has been stated is true, though the museums 

 of Europe contain vast collections gathered from all parts of 

 the earth, though the class itself is so rich in species that in 

 it, if anywhere, we might hope to find a complete series which 

 would throw light on the general principles of classification 

 yet the arrangement of insects into minor groups is by no 

 means placed on a satisfactory footing. The external parts 

 of insects have been examined with a minuteness and described 

 with a care which strikes the uninitiated with wonder. Not 

 only the shape of all the plates composing the rings of the 

 body, and the number and form of the joints of the legs and 

 antennae, have been made to yield characters for classification, 

 but even the number and shape of the joints of the appendages 

 of the mouth-organs, and the direction and number of the 

 nervures of the wings, together with the shape of the cells 

 which they circumscribe, have been impressed into the service 

 of taxonomy. Yet naturalists are far from agreeing in the 

 arrangement of insects into their larger groups. Some classi- 

 fiers place all insects under seven groups or orders, and some 

 are not contented with less than double that number. Con- 

 cerning the more conspicuous and independent insects there 

 seems to be a considerable agreement as to classification, and 

 these are comprised under seven orders. The additional orders 

 of those who make more orders than seven are made of minute 

 and generally parasitic insects. These, owing to the peculiarity 

 of their method of life, constitute what may be called aberrant 

 groups that is, groups which depart considerably from the 

 ordinary typical forms of insects. This idea of aberrant forms 

 will become clearer when we come to describe the several orders. 

 These aberrant groups of insects have been constituted into new 

 orders, or included under the older and better established orders 

 of the more conspicuous insects, according as each classifier 

 is more prone to dwell on the differences or the resemblances 

 of animal forms. 



Without going into the merits of the several systems, we 

 shall adhere to that classification by which all insects are 

 arranged into seven orders, because this system will probably 

 give to the reader a clearer idea of the different groups of 

 insects than the ampler system. We have therefore to dis- 

 tribute the aberrant groups among these seven orders, but in 

 so doing we shall call attention to them, so that the reader 

 may not be perplexed when he refers to other systems of 

 classification. 



The class Insecta is well defined by the following characters. 

 They are animals with well-developed jointed limbs, one pair 

 of antennas or head-feelers, compound eyes, feelerless upper 

 jaws (mandibles), a distinct head, a trisegmented thorax, to 

 which is attached three pairs of legs, and (normally) two pairs 

 of wings, limbless abdomen, and respiration by tracheae. 



The terms used in this classification will be understood by 

 those who have read the last lesson. The whole definition 

 is necessary, in order to cut off the insects from all the neigh- 

 bouring classes. Thus they possess jointed limbs in common 

 with centipedes, spiders, and crustaceans, but they are by their 

 character cut off from the worms. Centipedes (Myriapoda) 

 have one pair of antennae, as insects have, but this peculiarity 

 severs these classes from the spiders, which have no antennae, 

 and also from the crustaceans, which have two pairs. On the 

 other hand, the absence of limbs on the last division of the body, 

 while it is likewise characteristic of the spiders, completely 

 separates them from the myriapods and crustaceans. The 

 possession of two pairs of wings is peculiar to insects, but still 

 this is not a good distinctive character, because wings are 'not 

 found in all insects. 



Insects as thus defined may be divided into the following 

 orders, to each of which we affix the ordinal definition : 



1. Hemiptera (half -winged). Insects with imperfect meta- 

 morphosis, free prothorax, and suctorial mouths. 



2. Diptera (two- winged). Insects with perfect metamorphosis, 

 suctorial mouths, membranous naked fore-wings, and aborted 

 hind-wings. 



3. Lepidoptera (scale-winged). Insects with perfect meta- 

 morphosis, suctorial mouthed organs, and membranous fore 

 and hind wings, covered with close-set coloured scales. 



4. Hymenoplera (membrane-winged). Insects with perfect 

 metamorphosis, biting jaws, small ring-shaped prothorax, firmly 

 fastened by its upper part to the succeeding segment, and mem- 

 branous fore and hind wings, of which the latter are the smaller. 



5. Coleoptera (sheath-winged). Insects with perfect meta- 

 morphosis, biting jaws, free, strongly-developed prothorax, and 

 hard, horny fore-wings (Elytra). 



6. Neuroptera (net-winged). Insects with perfect metamor- 

 phosis, biting jaws, free prothorax, and membranous fore and 

 hind wings. 



7. Orthoptera (straight- winged). Insects without or with 

 imperfect metamorphosis, biting jaws, and the first segment of 

 the thorax united to the second segment. 



One thing should be noted in this ordinal arrangement which 

 otherwise might perplex the student. The Dragon-fly family, 

 with its nearly allied families of the Ephemeridae (May-flies) 

 and the Perlidae, are transferred from the Neuroptera to the 

 1 Orthoptera on account of their having a free prothorax. Now 

 the dragon-fly was once considered to be the very type of a 

 neuropterous insect, and it seems probable that Linnaeus 

 intended that it should be the type of the order he constituted; 

 nevertheless, it is certain that the dragon-flies and the may-flies 

 show a nearer relationship to the Orthoptera than the rest of 

 the so-called Neuroptera. 



The Hemiptera are so named from the fact that many of 

 them have their fore- wings distinctly divided into two parts ; 

 the anterior and outer half being horny, like the wing-cases 

 of a beetle, while the inner and hind half is membranous, like 

 the wing of a bee. 



As this peculiarity only belongs to one large division of the 

 order, some naturalists have given to it the name Rhynchota, or 

 beaked insects, on account of the long rostrum or sucking 

 snout which is found in every member of the order. 



The order is divided into two tribes, the Homoptera and the 

 Heteroptera. In the Homoptera (like-winged) the wings are 

 of the same consistency throughout. One of the largest and 

 most celebrated of these insects is shown in the illustra- 

 tion. The insect represented is the female. The male is 

 larger, and is furnished underneath with two large plates 

 covering in a musical apparatus, which it plies most vigorously 

 both during the day and night. The writer took this insect in 

 Italy, where it abounds, and has been known since classical 

 times. The ancients called the cicada happy, because it had a 

 dumb wife. The cochineal insect, the aphides whose periodical 

 presence in vast multitudes on plants is commonly called a 

 blight -the Chinese lantern-fly, and the froghopper, all belong 

 to this sub-order. Lice and bird-lice (Pediculina and Mallo- 

 phaga) may also be considered to be aberrant families of this sub- 

 order, though some have made separate orders for each of them. 



The Heteroptera (unlike-winged) have wings such as have 

 been described as giving their name to the Hemiptera. The 

 insect marked 2 in the illustration may be taken as a type 

 of this sub-order. The water-scorpion, the water-boatman, and 

 the hydrometra each represent families of this sub-order. The 

 last-named is represented in the engraving., It may be seen 

 skating over the surface of every piece of water in summer and 

 autumn. 



The Diptera may be divided into the flies proper and two 

 aberrant families. The lowest of these families is well known 

 to us, being represented by the almost ubiquitous flea. The 

 mouth-organs of this insect are very different from the genuine 

 flies, and in the place of wings they have only four scales, which 

 appear to be quite useless. Nevertheless, they appear from 

 their metamorphosis, and for other reasons, to be more nearly 

 allied to the Diptera than to any other order. The Pupipara 

 is the name given to other insects which are also parasitic and 

 wingless. These pass the whole of their larva state in the body 

 of the mother. 



The genuine flies may be divided into two great divisions, 

 one of which, the Brachycera (short-horned), have short antennas 

 composed of three joints, while the palpi are of one or two joints; 

 the other sub-order, named Nemocera (thread-horned), have their 

 whip-like antennae (sometimes beaded) in many joints, while the 

 maxillary feelers are four or five-jointed. The antennae also 

 often have fine secondary hairs springing from each joint, which 

 gives them the appearance of a plume. This, in the common 

 gnat, is a very pretty object. The common daddy-longlegs 

 (Tipula) is a good example of this order. Both of the flies in 

 the illustration belong to the Brachyeera. The hornet-fly is 

 one of the largest of our British Diptera, and while in flight is 

 very like the insect from which it derives its specific name. 



The Lepidoptera have been variously divided into groups. 



