SYSTEM OF INSECTS. 407 
genus. A departure, however, in only one respect from 
what may be called the normal characters of its group, 
does not annul the claim of any tribe of insects to remain 
in it; since this very often only indicates a retrocession 
from the type, and not a disruption of its ties of affinity. 
Thus the saw-flies (Tenthredo L.) differ from the other 
Hymenoptera, though not in their pupee, yet more or less 
in their larvee; but this alone cannot countervail their 
agreement with that Order in their organs of manduca- 
tion and motion, in their ovipositor, and in the other de- 
tails of their structure?. 
I have on a former occasion pointed out many of-the 
analogies which take place between insects and other 
parts of the animal kingdom, and even between insects 
and the mineral and vegetable kingdoms®: I shall now 
resume the subject more at large, but without recurring 
to those last mentioned. In considering the analogies 
which connect insects with other animals, or which they 
exhibit with respect to each other, we may have recourse 
to ¢wo methods. We may either consider them as placed 
somewhere between the two extremes of a convolving 
series, from which station we may trace these analogies 
upwards and downwards towards each limit; or we may 
conceive them and other animals in this respect arranged 
in a number of series that are parallel to each other, in 
which the opposite points are analogous. The first mode 
will perhaps best explain the analogies that exist between 
insects and other animals, and the last those between dif- 
ferent groups of insects themselves. I shall give an ex- 
ample or two of each method, beginning with the first. 
4 See above, p. 3/3—. b VoL. I. p. 7—. 
