GEOGRAPHICAL DISTRIBUTION OF INSECTS. 493 
of the different Orders to each other — The Coleoptera 
may be stated as forming at least 1 : 2 of our intire insect 
population; the Orthoptcra and Dermaptera as about 
1 : 160; the Hemiptera as 1 : 15; the Lepidoptera as more 
than 1:4-; the Neuroj)tera with the Tridwptcra as 1 : 29; 
the Hymenoptera as about 1:4; the Diptcra as not 1:7; 
and the Aptera and Arachnida as perhaps amounting to 
1 : 19 a . 
To extend this inquiry to exotic and more particularly 
to extra-European insects, in the present state of our 
knowledge, would lead to no very satisfactory results. 
The lists we have are so imperfect, that those which tell 
most in this country, — I mean the more minute insects 
and the Brachyptcra — have hitherto formed a very small, 
if any part, of the collections made out of Europe. 
Mr. W. S. MacLeay however, who, besides his father's 
(particularly rich in Petalocera), has had an opportunity 
of examining the Parisian and other cabinets, finds that 
the species of coprophagous insects within the tropics, to 
those without, are nearly in the proportion of 4- : 3 ; and 
that the coprophagous Petalocera, to the remainder of 
the saprophagous ones, may be represented by 3 : 2 b . 
It may be inferred, from the superabundance of plants 
and animals in equinoctial countries, that the number of 
species of insects in general is greater within than with- 
out the tropics : the additional momentum produced by 
the vast size of many of the tropical species must also be 
taken into consideration. 
II. There are three principal points that call for at- 
" If we consider the number of species of Acari, Nirmi, Poduras, 
and Araneid<E t this proportion will appear moderate. 
b Hor. Entomolog. 48. 
