GEOGRAPHICAL DISTRIBUTION OF INSECTS. 45 



specierum notas, chavacteres, nomina accuratissime dignoscas." 

 It would be fruitless for me, possessing so limited a knowledge 

 of species as I do, to attempt to point out the geographical 

 disti'ibution of either species or families: this also is far fi'om 

 my plan. I merely wish to point out, with the utmost diffi- 

 dence, in what I suppose others to have erred, and to show 

 what it is that our attention ought to be directed to. To detect 

 and avoid error is one step gained towards arriving at truth : 



Virtus est vitium fugere, et sapientia prima 

 Stultitia caruisse. 



Were we to follow the plan adopted by Humboldt, in his 

 excellent Prolegomena de Dist. Geog. Plant, we should 

 commence by estimating the total number of insects already 

 known, and proceed to calculate what portion of them belong 

 to the polar circle, the temperate zones, and the regions be- 

 tween the tropics, and also the relative proportions which the 

 different classes bear to one another in different latitudes. 

 But so little attention is paid by foreign collectors to any 

 classes but Lejndoptera and Coleoptera, that we are left with- 

 out any precise data on which to found our calculations. 

 Were we to judge from what we see of foreign insects, we 

 should be led to believe that these two classes increase in 

 number of species as we proceed from the poles towards the 

 equator much more than the other classes ; but this is greatly 

 to be doubted. Perhaps in the Hymenoptera, Diptera, and 

 Neuroptera, the countless myriads of individuals of particular 

 species which occur in the warmer regions, may have some 

 influence in diminishing the general number of species ; and 

 therefore there may be some reason for believing these classes 

 not to increase in an equal ratio with the others. Moreover, a 

 large proportion of the Neuroptera are aquatic in their larva 

 and pupa states, consequently these families are less likely to 

 be rich in species in regions like the intertropical parts of the 

 world, where almost every stagnant water, excepting the large 

 lakes, is evaporated during the dry season, and where most 

 of the smaller streams partake of the character of torrents. 

 We find aquatic insects to be in general much less influenced 

 by climate than terrestrial. In Coleoptera, the largest species 

 are inhabitants of the temperate zone ; and, of the three hun- 

 dred and twenty-three species of H ydrocanthares indicated 



