132 ZOOLOGY. 
The order includes the families, Scutigeridee, Lithobude, Scolopendride, — 
and Geophilide. 
The genus Scolopendra has four pairs of eyes, twenty-one seements, or 
twenty-two if the head is considered to be composed of two segments. In 
the latter case the segments may be made to correspond with the thirteen 
composing the body of insects, if the preescutum, scutum, scutellum, and 
postscutellum of each of the three thoracic segments, are counted separately. 
Under this view, the segment preceding the nine abdominal segments in 
Scolopendra will be the metathoracic postscutellum ; and the posterior 
division of the head will be the prothoracic preescutum. A similar division 
of the segments appears in Cryptops. 
The genus Scolopendra is widely distributed over the globe, the larger 
species (one of which is a foot in length) being peculiar to warm regions. 
Their bite is poisonous, and may be compared to that of the scorpions. 
Class 6. Insecta. 
The name of the class of Insects is derived from the znsected or articu- 
lated structure of the body, and its frequent division into several portions, 
as in the Hymenoptera. It has been variously applied to portions of the 
Articulata, but always including the hexapod orders, which are provided 
with wings in most cases, and to which the term has been more and more 
restricted. 
Insects are dioicous articulate animals, breathing air by means of trachee, 
and having a head and abdomen united by an intermediate thorax bearing 
the six feet and two or four wings when these are present. They have a 
free head bearing two antennee, and they are subject, during their growth, 
to certain external and internal changes termed metamorphoses. Most 
insects have wings, a peculiarity which none of the other classes possess. 
The integument is usually sufficiently hard to serve as a kind of external 
skeleton, to the inside of which various muscles are attached. 
The body of insects is usually considered to be composed of thirteen 
(sometimes fourteen) segments, which are apparent in the larva, although 
some of them are frequently so much reduced in size, or so intimately joined 
together, that they cannot be distinguished in the adult. The head forms a 
single segment, followed by the thorax, which is composed of three seg- 
ments, and the remaining ones belong to the abdomen. 
In Orismology, or the application of names to organs, it has become a 
matter of very great importance to apply the same name to the same part 
in different groups of animals, so far as this can be satisfactorily ascertained. 
The neglect of the older entomologists to observe a rule the advantages of 
which are so apparent, has been productive of much confusion, and we 
accordingly find the term thorax, which is correctly applied to the part 
between the head and abdomen of a ymenopter (pl. 79, jigs. 11, 14, 18), 
also employed to signify the segment next to the head in Coleoptera 
336 
