THE PRACTICAL ENTOMOLOGIST. 



75 



That this classification is in exact accordance 

 with nature Von Baer demonstrated, when follow- 

 ing close upon the researches of Cuvier, by inde- 

 pendent investigations into the growth of animals 

 he showed that the vertebrate embryo first deve- 

 loped a bony skeleton which gradually closed around 

 the nervous system and served as points of attach- 

 ment for the muscles; that the young mollusc first 

 appears as a simple sac or bag containing the viscera 

 lodtjed within, and it is comparatively late in life 

 that its shell grows about it; and that the young 

 radiate from the first shows a radiated structure, 

 while the young articulate first develops an outer 

 jointed body-wall, through which the stomach, 

 nerves and arteries can be seen gradually forming. 



The articulates are by far the most numerous in 

 species of either branch, the insects alone being 

 supposed to number upwards of 500,000 species. 

 The jointed worm seems to have been selected by 

 nature as afiijrding almost an infinity of modifica- 

 tions arising from variations in the number of rings, 

 their relative size, and in the number and form of 

 their appendages. 



The idea of articulation which pervades this im- 

 mense group of animals is seen best exemplified in 

 the worm. The earth worm is long and slender- 

 jointed, the body gradually tapers towards the head 

 and opposite extremity. (Figure 1 shows a cross 

 section of a worm.) 



Upon making a section of the body we find the 

 muscles attached to the inside of the body-wall, that 

 the nervous system — which consists of a single cord, 

 enlarging in each ring into a guaglion or nerve- 

 knot, which in the Crustacea and Insects is doubled 

 — rests upon the floor of the cylinder, the alimentary 

 canal occupies the centre, while above it just under 

 the back rests the heart or so-called dorsal vessel, 

 consisting of a tube which pumps the blood from the 

 tail towards the head, whence it flows in different 

 currents back through the general cavity of body 

 and returns in veins often incomplete. The breath- 

 ing apparatus is also tubular like the other organs 

 thus formed to pack closely in the tubular body. 

 In the higher worms the breathing tubes or bran- 

 chiae are placed around the mouth. Very diiferent 

 from these are the air tubes or tracheas of insects 

 which as in the figure (2 <j) enters through holes in 

 the side of the body above the insertion of the legs, 

 and ramify throughout the entire system, thus oxy- 

 genating the blood. 



There are three grand divisions or classes of ar- 

 ticulates, the Worms, Crustacea and Insects. 



The worm is long and slender, composed of an 

 irregular number of rings, all of very even size. 

 Thus while the svze of the rings is fixed, the number 

 is indeterminate, varying from 20 to 200 or more. 

 The outline of the body is a ungle cylindrical figure. 

 The organs of locomotion are fleshy filaments and 

 hairs (Fig. 1 /) appended to the sides. 



The Crustacean, of which the lobster is an exam- 

 ple, is composed of a determinate number (21) of 

 rings in the typical forms, which are gathered into 

 two regions, the head-thorax (cephalothorax) and 

 hind body or abdomen. In this class we have first 



introduced true jointed legs attached both to the 

 head-thorax and abdomen. In the Insects the rings 

 are arranged into three groups. 



The number of rings is twenty — seven in the head, 

 three in the thorax, and ten in the abdomen. Thus, 

 while in worms in which the abdomen greatly pre- 

 ponderates in size, the head is no larger than a sin- 

 gle ring of the body; in the Crustacea the head- 

 thorax is larger than the abdomen ; in Insects there 

 is the most equable proportion between the three 

 regions; the head in the highest insects being but 

 little smaller than the thorax, and the thorax not 

 much smaller than the abdomen. 



Thus the mass of organization is thrown for- 

 ward towards the head; the' organs of sense and 

 locomotion have their greatest development over the 

 organs which perform the functions of vegetable 

 life, such as reproduction, and respiration, and diges- 

 tion. Insects also differ from Crustacea in having 

 wings and tracheaj (Fig. 2^) of which the last serve 

 to aerate the blood inside the body, while in the 

 Lobster or Crab the gills are attached to the legs 

 on the outside of the body, and thus act very im- 

 perfectly as lungs. 



Size is an important element in classifying 

 articulates, as those whose forms are most com- 

 pact and consequently smallest, are in a general 

 sense physically and psychologically of the most 

 compact and of the finest quality, just as in man 

 it is the finest quality, and compactness, and 

 symmetry of structure that determines high intel- 

 lectual and physical ability. The earliest insects of 

 geologic ages were huge, vast, misshapen, entomo- 

 logical monstrosities like the mammoths and ich- 

 thyosaurus among vertebrates. The Honey Bee is 

 of the size and compactness that aflfords a ti/jK of 

 the highest physical and physiological development 

 among insects, and thus stands at the head of the 

 articulate series. The body is tough, compact, well 

 knitted together. Its nervous system approaches 

 nearest to that of vertebrates, as its brain is larger 

 and better developed than in other insects. Its lo- 

 comotive powers are immense, and its entire organi- 

 zation fits it for the highest grade of insect life. 

 Witness its marvellous instincts, its social habits, 

 the diff'erentiation of the individual into sexes, and 

 grades of sexes, for the better performance of the 

 varied duties of a large and vast colony; its useful- 

 ness to man; its vegetable diet; though not carni- 

 vous, abundantly able to withstand the attacks of 

 its enemies — all betokening the most equable deve- 

 lopment of the functions of both animal and vege- 

 table life. 



Contrast this with the Dragon fly and Ephem- 

 era, the lowest of insects. Their bodies are huge, 

 lengthened, their abdomen worm-like. They are 

 rapacious and carnivous. Their eggs are few in num- 

 ber. The young larvae and pupae pass their lives in 

 the water. There is a great inequality in the de- 

 velopment of the elements of their crust. 



In classifying insects we must steadily keep in 

 view the development and forms of the cni^t or 

 wall of the body, and nofthe organs alone, whicli 

 are but of secondary importance. 



