26 DEFINITION OF THE TERM INSECT. 
arrangement more difficult, since it will be impossible 
at the same time to connect the Myriapods with the 
Crustacea, and the Trachean with the genuine Arachnida. 
I admit the validity of your objection, but by no arrange- 
ment of insects in a simple series can we attain this object: 
the difficulty, however, may perhaps be obviated in this 
way. The distribution of organized matter, to adopt 
Mr. Wm. MacLeay’s metaphor?, begins in a dichotomy, 
constituting the animal and vegetable branches of the 
great tree of nature, and from these two great branches, 
by means of infinite ramifications, the whole system is 
formed, and, what is remarkable, these branches unite 
again so as to represent a series returning into itself, a 
discovery due to the patient investigation and acumen of 
our learned friend just mentioned. Now, in considering 
the Aptera order, we find at first setting out from the 
Hexapods, a dichotomy, where the Anoplura Leach 
branch off on the one side, and the Thysanura Latr. on 
the other—the former, by means of the Pediculida, tak- 
ing their food by suction, particularly Phthirus Leach, 
or the Morpion (in which the segments of the trunk and 
abdomen become indistinct) approach the Octopods by 
the hexapod Acarina—the latter by Machilis polypoda 
tending towards the Myrzapods. In the Octopod branch 
a further dichotomy takes place, from which you proceed 
on one side to the Aranezde in the Arachnida, by Pha- 
langium, &c.; and in the other by Chelifer, &c. to Scorpio. 
Again, the Myriapod branch also divides, going by the 
lulid@ to one branch of the Isopod Crustacea, and by the 
Scolopendride to another. 
But there is another view of this subject before alluded 
* Hor. Entomolog, 134. 200. 
