34 NATURAL HISTORY OF WASPS. 
* Facies non omnibus una, 
Nec diversa tamen: qualem decet esse sororum.” * 
Distinctions of colour and markings, like the differ- 
ences in the handles of our tools, in the labels on 
our books, or even in the blots of ink on their covers, 
are of value as affording a ready means of recogniz- 
ing the different species at a glance. We see what 
wasp, or what book we have, at once, from .the out- 
side marks, without looking inside. They are of 
value when they have been shown to have a certain 
connection with the peculiar habits and internal 
structure of certain species, because they are more 
open to observation than these habits and structure. 
Their value diminishes in proportion as they are more 
difficult to observe, or less constant; till, though they 
are curious, and may have a local interest, they cease 
to be of any practical importance, as a means of 
classification. 
Distinctions of this kind, to be of any use, should , 
be very exactly laid down; and this must be my 
excuse for devoting so much space to what may 
appear a very trifling matter. With the help of 
drawings, or labelled specimens, the distinctions are 
easy enough to trace; but, without them, mere verbal 
descriptions are of little use. The parts which bear 
the characteristic markings are the clypeus; the 
neighbouring parts of the face, with the scape of 
the antenne; the dorsal surface of the thorax at its 
posterior portion ; and the dorsal surface of the first 
two or three abdominal rings. I propose to point 
out the characteristic marks which are to be found in 
each of these parts respectively in the several species, 
* Ovid. ‘Metam.’ II, 13. 
