cominon to North America and Europe. 479 



sufficiency of the standing arguments against it, and the 

 necessity of a thorough revision of them, than to take a 

 decided stand (upon a question which I regard as open to 

 further discussion) before its facts have been carefully ob- 

 served, or the resulting generalizations properly deduced ; so 

 that, whether it be admitted or not, it is entitled to the benefit 

 of all the discoveries which can be brought to bear upon it; 

 and, on this account, I have not hesitated to give a slight 

 sketch of the theory of transmutation, as I conceive it to be 

 modified by some of the results of modern science.* 



I had intended to prepare a list of insects common to 

 Europe and North America, to be presented on the present 

 occasion ; but, as our collections are not in a condition to ad- 

 mit of such an undertaking, and as such a list would have 

 contained the names of a number of species which have 

 probably been introduced through human intervention, (as 

 Bruchus pisi or Dermestes lardarius) I resolved to take some 

 family of nearly equal distribution upon both continents, and 

 which had been pretty thoroughly studied. For this purpose, 

 I have chosen the Brachelyira, most of the species of which 

 are small, and of such habits as to prevent them from being 

 readily introduced artificially. 



Of this family, Erichson, the highest authority, enumerates 

 220 North American (exclusive of Mexican) species, of which 

 12, or five and half per cent., inhabit Europe. But recent 

 discoveries raise our species to 250, of which none of the 

 additional ones have been identified as European, (perhaps 

 from inability to institute comparisons) ; on the strength of 

 which, we may reduce the percentage io Jive, when a remark- 

 able coincidence is apparent with that already assigned to tlie 

 Physadse. Of the genus Philonthus, 22 American species 



* These views have been held by men of learning and piety at various times. 

 Thus Ray and Swammerdam believed that the parasitic hymenoptera, to which a 

 dead caterpillar apparently gives birth, may result from the division of its vitality 

 into numerous portions, and no one finds fault with the "evil tendency "or "ab- 

 surdity " of the idea. Now, the objection appears to rest not so much against the 

 opinion as the source whence it comes; in other words, Ray was an Englishman, 

 whilst Larnarck was a Frenchman. 



V 

 V 



