2 NOTES ON 
(Arachnoidea) ; crustacea; mites (Acar?) ; and 
centipedes (Myriapoda*) ; which were included 
among the apterous, or wingless insects. This 
rejection has been made from a more accurate 
examination of their internal organization, and 
the word insect is now confined to animals whose 
respiration is performed by two trachee, or air- 
tubes, which run parallel to each other, the 
whole length of the body, occasionally sending 
off ramifications. These receive and emit the 
air through apertures (stigmata), placed at inter- 
vals along the sides, or near the tail. As air- 
vessels pervade the body, a complete circulation 
of a vital fluid is not required, its eration being 
effected by air carried to it, and is not, as in the 
larger animals (vertebrata), collected into one 
great vessel, and then subjected to its action. 
Some observations on this subject, with illus- 
trative engravings, will be found in chapter 3 
of the new edition of the “ Microscopic Illustra- 
tions.” 
The nervous system is composed of two 
cords, united at certain distances, where an 
enlargement (ganglion) occurs, which sends off 
various branches to the surrounding parts. The 
head in insects is distinctly separated from the 
* These are still included (but in a distinct order) by Cuvier. 
