OP ANIMALS. 51 



are called mandibles and often palpi, articulated filaments, 

 which appear to serve in recognizing their food: in the second, 

 there is a proboscis for suction. The organs of digestion are 

 complicated and various. They enjoy the sense of smell, but 

 its seat is not well determined. They have all an abdomen, 

 and a thorax which supports six articulated feet, at least. Their 

 skin is encrusted and solid,each articulation of the feet is tubular 

 and contains the muscles of the succeeding one. All the ar- 

 ticulations <K the feet are by gynglymus; generation is sexual 

 and oviparous. This section contains three great classes, that 

 of insects, the arachnides, and the Crustacea. 



42. Insects, or the hexapoda, have the body composed of 

 segments or numerous rings, and divided into three principal 

 parts, six articulated feet, a distinct head furnished with eyes, 

 and two antennae, a thorax which supports the feet and wings, 

 when there are any, and an abdomen which contains the prin- 

 cipal viscera. The mouth is very complex, in the grinders, 

 there are lateral jaws, in the suckers there is a proboscis. The 

 intestinal canal more or less long, enlarged, contracted, &c,, 

 terminates by an anus. There is a vestige of a heart in a vessel 

 attached along the back, divided into segments by strangula- 

 tions, and which experiences alternate contractions. The fluid 

 it contains is white, and appears to penetrate it, like the rest 

 of the body, by imbibition. Respiration is effected by means 

 of ramified tracheae united in two principal trunks. The se- 

 cretory organs consist in long spongy vessels or canals, dou- 

 bling on themselves, running through the mass of the body, 

 and ending either in the intestine or elsewhere, according to 

 the uses of their products. The sexes are separated most fre- 

 quently, the genital organs terminate in the anus. These ani- 

 mals copulate but once in their life. The impregnated female 

 deposits her eggs in a suitable spot, and the eggs produce ver- 

 miform animals called larvae, which changes into a chrysalis, 

 a state of apparent death; and from which emerges the perfect 

 insect that soon propagates its species and dies. This consi- 

 derable change of external form, accompanied by others more 

 or less great in the structure, is called a metamorphosis; all in- 

 sects, the thysanouraand the parasiticaexcepted, which by their 



