On the Geographical Distribution of Insects. 343 



form the half of these 7400 plants above mentioned, and that 

 the same insect often Uves at the expense of several plants, it 

 will be admitted, that the allowance of three insects for each 

 plant is a reasonable proportion. It may be alleged that the 

 proportion must be greater under the tropics, and this is pro- 

 bably the case with phytophagous species ; but, on the other 

 hand, there is a deficiency of creophagous kinds, which restores 

 the equilibrium. Now by estimating, with M. Decandolle, the 

 total number of existing vegetables at from 110,000 to 120,000, 

 we obtain from 330,000 to 360,000 for that of insects.* 



It is more dif&cult to determine how the above number 

 ought to be divided among the different orders, for this cal- 

 culation can only be founded on the species existing in col- 

 lections ; and it is well known that some departments have 

 been much more assiduously cultivated than others. The fol- 

 lowing is the result of our author's inquiries on this subject. 



Fifteen years ago, Mr Macleay estimated the amount of 

 species preserved in collections at 100,000. This number was 

 adopted by Latreille ; but our author conceives that we should 

 be much nearer the truth by lowering it, as has been done by 

 Dr Burmeister, to 80,000. Of this number the Coleoptera 

 must form nearly one-half ; for very little short of 30,000 are 

 contained in the Parisian cabinets alone, and many others 

 must exist in different places, by the union of which, at least 

 40,000 would be attained. In making this calculation, we 

 ought to keep in mind the unequal manner in which exotic 

 species arrive in Eiu-ope. Thus, Paris and Berlin receive 

 principally those of America ; the species of the Sunda and 

 Molucca islands go chiefly to Holland ; England receives them 

 from New Holland and Bengal more than from other coun- 

 tries, &c. The exchanges which entomologists make with 

 each other remove but imperfectly this original inequality. It 

 therefore follows that every country possesses, in some degree, 

 peculiar exotic species ; and consequently, we will arrive at a 

 higher number by uniting the collections existing in all, than 

 if we draw our inferences merely from the collections of any 

 one country. 



• Kirby and Spence, by a similar calculation, make the number 400,000, 

 which appears rather too high. 



