70 



THE LANCASTER FARMER. 



[Mcy, 



WHAT IS AN INSECT?* 

 Among the masses of mankind, or popularly 

 considered, an Insect appeats to be any small 

 animal for which no other name "comes 

 handy," but, entomologically restricted, and 

 qualified by certain exceptions, an insect is a 

 four-winged hexapod, the body of which is con- 

 spicuously divisible into three transverse sec- 

 tions, namely the' head, the thorax and the 

 ahdomen. Although the body of an insect is 

 so easily divisible, that if we strike against a 

 pin upon which a very dry specimen is im- 

 paled, it will be very apt to fall mto three 

 pieces ; yet a closer inspection will reveal the 

 fact that these are not simple or solid pieces, 

 but that they are all compound, and composed 

 of many minor parts. Take the abdomen for 

 instance, and it will be found to consist of a 

 series of sections or rings called segments, or 

 by way of distinction, abdominal segments. 

 Neither are these rings entire in their struc- 

 ture, but are latterly divisible into semi-rings, 

 the upper ones called dorsal and the lower ones 

 ventral The thorax, to which are attached 

 the wings and the feet, is also a compound 

 section, being composed of prothorax, meso- 

 thorax and metathorax, and like the abdomen 

 laterally divisible — the upper parts intojjrono- 

 tum, mesonotum and metanotum, and the lower 

 parts into prosternum, mesosternuni and me'.as- 

 terniim. In some orders of insects—notably 

 the order Coleoptera, beetles — the dorsal divi- 

 sions of the prothorax are confluent, that is, 

 they are united into one solid piece, whilst 

 the ventral portion is compound ; not only 

 divisible into three parts, but into many more. 

 There are also some minute species in the 

 order Aphanipteka, or wingless insects, in 

 which the thorax and the abdomen are confluent, 

 and the insects seem to possess only a head 

 and abdomen, the thorax being conspicuously 

 absent, or if present at all, only rudimentally 

 so. The head of an insect is still more com- 

 plicated in its structure, and the parts more 

 numerous than in the other divisions of the 

 body, and this is especially the case in mandi- 

 hidated insects, that is, those possessing Jaws, 

 and their usual accompaniments. In short, 

 Monsieu Straus has enumerated in the body 

 of an insect not exceeding an inch in length, 

 306 liard pieces, which enter into the compo- 

 sition of the outer envelope ; 496 muscles for 

 putting tliosein motion ; 4S nerves to animate 

 them, and these nerves divided into innumer- 

 able fillets ; also 4s pairs of trachie, or breath- 

 ing organs, equally ramified and divided, to 

 convey air and life into "this inextricable 

 tissue." These are the little animals popu- 

 larly despised, and yet have the power to 

 scourge mankind with fear and famine. 



But, an insect is something more than a 

 "four-winged hexapod." It occupies not 

 only an important position in the economy of 

 nature, but also quite as important a one in 

 systematic classification. There are many 

 systems of classification ; but, perhaps that of 

 CuviER, the great French naturalist, is the 

 most popular, as it is certainly the most 

 simple. He divides the animal kingdom into 

 four sub-kingdoms, namely : Anamalia verte- 

 Irata, that is, animals possessing a vertebral 

 column or backbone ; Animalia mollusca, ani- 

 mals destitute of a backbone, but possessing 



♦Essay read before the Linnnean Society atita meeting: 

 on Saturday, April 28, by Dr. S. S. Eathvon. 



an external shell, either univalved, bivalved 

 or multivalved; Animalia articulata, animals 

 possessing a greater or lesser number of con- 

 secutive rings, sections or segments, united 

 by ligaments in a series of articulations or in- 

 sected joints ; and Animalia radiata, em- 

 bracing those animals known under the name 

 of Zoophytes, the organs of sense and motion 

 of which are disposed as divergent rays round 

 a common centre. Of course this is but a 

 simple outline of the structure of the animals 

 classified in the four sub-kingdoms named ; 

 and is only cited here to illustrate where, in 

 the series the class including insects stands, 

 and its relation to other cla.sses. Cuvier 

 further divides the sub-kingdom Articulata 

 into two great sections or groups, namely : 

 the Apiropoda — animals po.ssessing more 

 than six feet, and destitute of wings, including 

 the Crustacce, the Aruchinice and the Mtjriapoce, 

 or crabs, spiders and centipedes. The second 

 section or group are the Hexapoda, animals 

 with six feet ; and, including the single class 

 Insecta, from which it will be observed that 

 we locate insects at tRe foot of the sub-king- 

 dom Articulat.\ ; and it may also be ob- 

 served that although crabs, lobsters, scorpions, 

 spiders and centipedes are Articulates, they are 

 not, therefore, insects. This is the entomo- 

 logical restriction to which, in part, I al- 

 luded in my opening lines Entomology 

 is derived from two Greek words, namely : 

 entom, and insect, and logos, a discourse. The 

 word Entom, as well as the synonymous Latin 

 word insectum (which has beon anglicised into 

 insect), are themselves compounded of other 

 words, signifying a cutting or dividing into 

 sections or articulations, whence, in fact, we 

 arrive at one of the great characteristics of 

 these tribes of animals : namely, the articu- 

 lated structure of the external parts of the 

 body, which may be properly regarded as the 

 skeleton, serving, as it does, to support the 

 muscles and other internal organs, just as the 

 internal skeleton of the liigher, or vertebrated 

 animals, support corresponding parts. 



It may be well to state here that the hexa- 

 podal character of insects relates to the per- 

 fectly developed form of the animal, after it 

 has passed through all its transformations or 

 transitions, corresponding to a, metamorphosis ; 

 for, it must be remembered, that the life 

 of the insect consists of four very distinct 

 phrases of development. First we have the 

 om, or egg, which contains the embryo of the 

 future animal. After the period of incuba- 

 tion is accomplished, the insect is technically 

 said to be excluded from the ova, when it issues 

 forth, in some orders, altogether unlike the 

 parent that deposited the egg. The popular 

 names applied to these animals after their ex- 

 clusion from the egg are many, such for in- 

 stance as caterpillars, worms, grubs, slugs, 

 maggots, bots, etc., and in many cases these 

 have a qualifying prefix, as horn-worms, corn- 

 worms, boll-worms, canker-worms, army- 

 worms, wood-worms, pear-slugs, rose-slugs, 

 grub-worms, sheep-bots, cattle-bots, horse- 

 bots and many others ; but, scientifically, all 

 these forms are included under the simple term 

 larvcv. The term larva means a mask. An 

 insect after it has left the egg and before it 

 assumes the form of a pwpa or' chrysalis, is 

 called a larva, because in that state it is, as it 

 were, masked. This rule does not, however, 



apply to all the different orders ; for the 

 change in form in some of them can hardly 

 be called a distinct raetamophosis, but rather 

 seems to be a gradual transition, exibiting 

 very little distinction between the larva, the 

 pupia and the imago or mature form. In the 

 larva state we also encounter the exceptions 

 to their hexapodal characters, riome larva: 

 are entirely destitute of feet, others possess 

 them only rudimentally ; • same have only 

 four, some six, some eight, some ten, twelve, 

 sixteen and up twenty-two, but these exceptions 

 could only be noticed specifically in treating 

 of the diflferent orders separately. I might 

 mention. However, by way of illustration that 

 in the larvfe of Ortiioptera (grasshoppers) 

 for instance, there are never more or less than 

 six feet, whilst in those of Lepidoptera 

 (butterflies and moths) there are never less 

 than ten, nor more than sixteen. But in all 

 that have feet at all, tliat are present either 

 perfectly or rudimeutally six, they are called 

 pectoral feet, on tlie first three anterion seg- 

 ments of the body. The termpectoraZ is from 

 the Latin pectoris, and relates to the thorax 

 or chest. These three segments are rudimen- 

 tally the future prothora.c, mesothorax and 

 meatliorax of the perfect insect, and have 

 already been referred to in this paper. The 

 remaining feet are more or less developed — 

 wart-like — tubercles, called prolegs, and in 

 some orders are more prehensile than the 

 pectorals. 



There is no uniformity in the duration of 

 the larval periods of insects. This is governed 

 by species and surrounding circumstances. In 

 some species it continues only a few days, in 

 others it is prolonged to weeks, to months, 

 and to years — in the seventeen — years Cicada 

 (commonly called " Locusts"), for instance, 

 to nearly or quite seventeen years. That which 

 comes out of the ground, and from which the 

 mature insect is evolved, is not the larva, it is 

 the pupja; but there is reason to believe that 

 it only assumes the pupal form a few weeks 

 before its final evolution. I have obtained 

 them in the months of February and March 

 immediately preceding their septendecenial 

 appearance, and they were still in the larval 

 form. During the larval period of insects, 

 they moult orcastofl: the external integument 

 from three to six times, the most familiar il- 

 lustration of which, is in the larval develop- 

 ment of the "Silk worm." At the end of 

 this second stage of insect development comes 

 the third or pupa state, in which there is as 

 little uniformity as there was in that which 

 preceded it. In some orders it is a quiescent 

 itate, in which no food can be appropriated — 

 the animal is fixed and cannot locomote ; but 

 in others, the pupa is as active in this state, 

 as it is in the larvaj state, and quite as vora- 

 cious. ■ Pupa is a Latin term, and means a 

 puppet, or baby, wrapped up in swaddling 

 clothes. In some pupce the future insect may 

 be distinctly recognized, especially as to the 

 wings, the feet, the antennre, the eyes, and 

 the rostrum or sucking tube. Some are en- 

 tirely naked, and others are enveloped in a 

 cocoon ; some are elevated above the earth ; 

 and others are buried beneath the earth ; 

 some are concealed within the cavities or 

 galleries cut in timbers or other substances 

 by the larvfe, and others are suspended by 

 their caudal extremities being attached 



