4 J 6 SYSTEM OF INSECTS. 
mediate direction, it matters not), it cannot be satisfac- 
torily ascertained but by considering attentively the gra- 
dual approximation or recession of the structure to or 
from a certain type in any point of such series. If, there- 
fore, you wish to ascertain whether the characters, in 
which any given object resembles other objects in certain 
groups, indicate affinity or only analogy, you must first 
makeyourself acquainted with the common features which 
distinguish the animals known to belong to that group, 
— either those relating to their structure, or to their 
habits and economy. If the object under your eye par- 
takes in these characters more or less, in proportion as 
it approaches the type or recedes from it, the relation it 
exhibits is that of affinity ; but if, though it resembles 
some members of it in several points of its structure, it 
differs from the whole group in the general features and 
characteristic marks that distinguish it, the relation it 
bears to those members is merely that of analogy. Thus, 
for instance, Ascalaphus italicus in its antennas, the co- 
louring of its wings, and its general aspect, exhibits a 
striking resemblance to a butterfly ; yet a closer examina- 
tion of its characters will satisfy any one that it is in quite 
a different series, and has no ciffinity whatever to that 
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 (Serrifera) differ from the other Hy- 
menoptera, though not in their pupae, yet more or less 
in their larvae ; but this alone cannot countervail their 
agreement with that Order in their organs of manduca- 
