British Species of Caddis-flies. 7 
carefully traced out, as this differs considerably in different genera, 
“but much more so in some families than in others. I have en- 
deavoured to render this latter subject more readily comprehen- 
sible by giving outline figures of the neuration of each genus. In 
the larger forms, the neuration can be readily traced by the aid of 
an ordinary lens, but in the smaller it is necessary to use a com- 
pound microscope with a low power object-glass (a ‘ three-inch”’ 
is sufficient for all ordinary purposes), taking care to entirely 
denude the wing of its hairy clothing, and to place the detached 
wing on a glass slide, and cover it with a piece of thin micro- 
scopic glass, so as to flatten it out. ‘The transverse veins are 
the most difficult to discriminate, but at the same time furnish 
most important characters. Lastly, the general shape of the 
wings and other minor differences must be taken into account. 
Specific characters. 
The Trichoptera have suffered, perhaps more than other insects, 
from ignorance of the existence of characters whereby most of 
the species may be separated almost without a possibility of error. 
Many of them vary greatly in coloration, and as this was at one 
time the chief character attended to by descriptive writers the 
number of synonyms is something alarming. 
Rambur was the first to point out that in the parts subservient 
to the procreation of each species there are to be found structural 
characters of the utmost value, which had been almost entirely 
overlooked. ‘This step in advance was further greatly extended 
by Dr. Brauer, and since much more so by Dr. Hagen. Such 
indeed is the importance of these structural characters, that it is 
absolutely necessary that all descriptive works on new species 
should give full details of these parts, and, if possible, figures 
also. 
It is in the males that the anal appendices and generative 
organs are most prominent and present the most appreciable 
specific characters. (Rambur erroneously states the contrary.) 
The arrangement of these appendices, &c., varies so greatly in 
different genera, and even sometimes in different species of the 
arrangement of the nervures in the Trichoptera is very little prone to variation 
in different individuals of the same species, still occasionally specimens are 
found in which some of the transverse veins are absent, or additional ones in- 
serted, and even the longitudinal veins sometimes depart from the ordinary 
plan. However these are rare occurrences, and not likely to mislead the 
student, An extreme instance is figured at Plate IV. fig. 2. 
