On the Geographical Distribution of Insects. 183 



same ; it is thus that Spain and the coasts of Syria, or, if we 

 desire a still more striking example, France and the parts of 

 Siberia situate under the same parallel, possess a multitude of 

 common genera with species almost precisely similar. Finally, 

 if these regions are separated by an immense interval and by 

 natural banners, nothing continues common to them but the 

 families. Thus Tucuman and the shores of the Caspian Sea 

 have the greatest resemblance to each other in respect to soil, 

 which is arid, saline, and abounding in plants producing soda ; 

 both are likewise very rich in melasomes, but not one either 

 of the genera or species is identical. 



It is this diversity, produced by distance, which gives to each 

 region its proper entomology ; but at the same time the coun- 

 try reacts, in some degi-ee, on the species, by giving them a 

 peculiar /ace>*', which reveals their origin often at a first glance. 

 An entomologist, with an experienced eye, will frequently be 

 able to say of an insect presented to him, and which he had 

 not before seen, whether it be American, African, or Asiatic, 

 as readily as a botanist can do the like, in most cases, with 

 plants ; but it will be understood that this intuition is not of 

 such a nature as to be explained by words. 



(To be concluded in next Number.) 



On the Inflammable Gases of the Prussian Coal-Mines. By 

 Professor Gustav Bischof.* 



The Financial Department of our Ministry intrusted to me 

 the investigation of the inflammable gases occurring in the 

 Prussia?! coal-pits, and directed me also to make experiments 

 on the action of Davy's safety-lamp in explosive atmospheres. 

 During the last autumn, I collected inflammable pit-gas, per- 

 fectly pure, as it issues from the fissures in Gerhard's level, 

 and in an old abandoned level at JVellestveiler. At the same 

 time, by means of an apparatus, into which I could at plea- 

 sure introduce explosive mixtures of various degrees of inten- 



* From <a letter addressed to Privy- Councillor "\'on Leonhard. Translated 

 from Leonhard and Bronn's Jahrbuch for 1839, part 6. 



