570 INVESTIGATION OF INSECTS. 
their habitat and localities, or the source from which you 
derived them. In this you should number the genera in 
Roman capitals, and the species under each by a figure; 
leaving considerable space at the end of each genus for 
the insertion of new species. The other book should be 
of an octavo size, containing 400 or 500 pages. Under 
the number of each genus and species you might de- 
scribe and figure it, if undescribed ; if described, note in 
what it varies from the description, and what characters 
are overlooked: and in general, insert such observations, 
with regard to its economy and habits, as you may have 
had an opportunity of making. — As to foreign insects, 
wherever you can, upon good authority, be particular in 
indicating the country and station of each specimen. 
I need not say much to you concerning the micro- 
scopes you should use for the examination of insects, a 
common pocket one of three glasses of different powers 
will answer every ordinary purpose 3 . 
We have treated hitherto of insects as we find them 
now inhabiting our globe : but I must not conclude our 
correspondence without taking some notice of those that 
are found in a, fossil state. Fossil insects may be divided 
into those that are found in amber, and those that are 
found in other substances. 
It has been observed with respect to insectiferous am- 
ber, that the greater part of the insects found in it exist 
no longer in the countries that produce that amber, and 
that in every different locality the insects found in it are 
a For dissections the one recommended above, p. 201, may be 
used. Sometimes a watchmaker's eyc-glar.s, wlik h also sets the hands 
at liberty, will be found useful. 
