7074 Insects, 



a purpose ; and as they seldom give any clew to the size of their 

 insects, this circumstance alone, in many instances, renders discrimi- 

 nation impossible. 



It is a well-known fact that humble bees, being all densely clothed 

 with hair, are subject to extremes of variation, through bleaching by 

 exposure to the sun, &c. This, however, is not the only difficulty : 

 two of our most abundant species of brown bees, B. Muscorum and 

 B. senilis are frequently so closely alike that none but a practised eye 

 can detect their differences, and yet the former of these runs into 

 innumerable varieties, so much so as to»induce Kirby to create eight 

 species out of them ; the latter, B. senilis, only differs in being more 

 or less pale. On the other hand some species seldom, if ever, vary ; 

 in B. Hortorum, for instance, a species found in all parts of Europe, 

 specimens of which I have seen from Lapland, Finland, Denmark and 

 the South of France, I cannot detect any sensible difference ; others, 

 from the regions of Arctic America, exactly correspond with examples 

 taken in the vicinity of the metropolis. 



Fabricius has described, in the * Systema Piezalorum,' thirty-three 

 species of European Borabi, only nineteen of which are, in my opinion, 

 entitled to that rank ; the remaining fourteen being either varieties, 

 males or workers of the former. Many of these it would be impossible 

 to assign to the species to which they really belong without an exami- 

 nation of the typical specimens of the insects described ; fortunately 

 this has been accomplished, in several instances, by Dr. Nylander and 

 M. Drewsen, of Copenhagen. To both these eminent Hymenopterists I 

 am greatly indebted for information, which has, in a considerable 

 degree, reduced the difficulties which stood in my way. 



Having found an examination and comparison of the male generative 

 organs an unfailing guide in the determination of the species in the 

 family Vespidae, I determined to test its value in the discrimination 

 of the species of the genus Bombus, and the results have proved most 

 satisfactory ; in general, the differences of form are most marked and 

 decisive, and it is only in one or two cases that the differences are 

 slight ; but even then I consider them satisfactory : the species 

 between which 1 have found the slightest differences are B. terrestris 

 and B. Lucorum. There is not a single species which has not under- 

 gone such an examination ; and in order to test the constancy of form 

 in the male organs I have, in the cases of B. Muscorum, B. lapidarius 

 and B. Hortorum, examined from thirty to forty of each species, and 

 can therefore confidently attest the value of such investigations and 

 comparisons. The results contained in this paper cannot, I am aware 



