414 EXTERNAL ANATOMY OF INSECTS. 
gies that hold in this respect between the different tribes. 
Thus the Coleoptera are analogous to the Heteropterous 
Hemiptera ; the Orthoptera, with the exception of the 
Mantide, to the Homopterous Hemiptera ; the Mantide 
to the Lbellulina ; the Lepidoptera to the Trichoptera ; 
the Hymenoptera to the Diptera, with a slight variation, 
and probably others might be traced. 
viii. A word or two upon the motions of which the 
head of insects is capable. MM. Cuvier, in the extracts 
lately laid before you, speaks of different powers of move- 
ment as the result of different configurations of the parts 
of the head. ‘This probably is correct with regard to 
many cases; but a great deal will depend upon the power 
the insect has of protruding its head and disengaging 
its base from the restriction of the prothorax ; for where, 
like many ground beetles (Eutrechina), the Staphylinida, 
&c. itis able to do this, it can probably move its head in 
every direction. It is only where the ligaments are less 
elastic, or allow of little tension, that its movements are 
confined ; and few living insects have been sufficiently 
examined to ascertain how far this takes place. In those 
cases belonging to the ¢hird section of articulations, in 
which the head moves upon the thorax as upon a pivot, 
as is the case with Hymenoptera and Diptera, the move- 
ment is nearly versatile. I have seen a fly turn its head 
completely round, so that the mouth became supine and 
the vertex prone; and from the form and fixing of the 
head, it should seem that those of the Mantide were 
endued with the same faculty. 
ix. The parts and appendages of the head are now in 
