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 Myriapod es 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 Aracknides 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, 
Tracliiana, the respiratory organs resemble those 
of insects, and the circulation is therefore less perfect. 
The Crustacea , agreeing in very many points with 
