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 Orthoptera and Dermaptera as about 

 1 : 160; the Hemiptera as 1 : 15; the Lepidoptera as more 

 than 1:4; the Neuroptera with the Trichoptcra as 1 : 29; 

 the Hymenoptera as about 1:4; the Diptera as not 1:7; 

 and the Apt era 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 Brachyptera 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- 



a If we consider the number of species of Acari, Nirmi, Podurce, 

 and Araneidce, this proportion will appear moderate. 

 b /for. Entomohg, 48. 



