EXTERNAL ANATOMY OF INSECTS. 41] 
that the general conformation in this respect belonged 
to our learned author’s second mode of solid articulation, 
resembling that of the majority of the weevils (Rhynco- 
phora), in which the head has no projecting angles or 
tubercles, or other elevation, but is received usually 
into the circular cavity of the prothorax. 
His third mode of this articulation, that of the Hy- 
menoptera and Diptera, is so peculiar, that it ought to 
be considered as a primary kind; since in this the head 
moves upon the prothorax as upon a pivot, and has a 
kind of versatile motion. 
With regard to his fourth mode, which from his de- 
scription appears to be that of Apoderus, he allows mo- 
tion to the head only in one direction, observing that the 
lower margin of the prothoracic cavity has a notch. But 
M. Latreille calls the articulation of the head in this 
genus an Enarthrosis*, which admits motion in every 
direction; and if you examine the common species (A. 
Coryli), you will find that the prothorax has a sinus taken 
out of its upper margin, as well as out of its lower one— 
which at any rate will allow a motion upwards. 
I merely mention ‘these little maccuracies, with due 
diffidence, as some apology for giving you a different 
and at least a more popular and general view of this 
part of my subject, which I shall now proceed to state 
to you. It seems to me most convenient for the Ento- 
mologist, and most consonant to nature, to divide in- 
sects, with respect to the articulation of the head with 
the trunk, into three primary sections, each admitting 
one or more subdivisions. 
* Gen, des Crustac, et Ins. ti. 246. Regne Anim. iii. 325. 
