ENTOMOLOGY. 69 



allied races with which insects have any chance of 

 being confounded. To render this the more obvious, a 

 brief notice may be taken of a few of the more promi- 

 nent peculiarities presented by each of the other arti- 

 culated classes, when compared with that in question. 

 The Myriapodes make by far the nearest approach 

 to them in essential properties, the internal structure 

 being almost identical, while many of the external 

 parts are similar : thus there are generally two com- 

 posite eyes, two antennae, and oral organs similar to 

 those of masticating insects. The differences, how- 

 ever, are sufficiently striking, and consist of the 

 numerous segments, without any division of the body 

 into thorax and abdomen ; in the number of feet, 

 always exceeding six, and sometimes amounting to 

 two hundred ; and in the body acquiring with age 

 an increase in the number of the component segments. 

 The Arachnides generally have the head soldered to 

 the thorax, and many of them seem to have no other 

 incisure than that which separates the thorax from 

 the abdomen ; no antennae nor composite eyes ; more 

 than six feet, and the generative organs placed, with 

 very few exceptions, under the belly before the 

 middle. In that section of them named Pulmon- 

 aria, after the air has been admitted by stigmata, it 

 is received by a kind of sacs, analogous to the lungs 

 of vertebrate animals, and the circulation in con- 

 sequence is pretty complete ; in the other division, 

 Trachiana, the respiratory organs resemble those 

 of insects, and the circulation is therefore less perfect. 

 The Crustacea, agreeing in very many points with 



