150 THE HUMBLE-BEE vill 
munities, and, in three of the cases, is of a larger 
size than the northern form. 
The relationship between £L. derrvestris and B. 
lZucorum, and that between B. vruderatus and B. 
hortorum are closer than in the cases of the other 
two couples; but although these four forms are 
abundant over the greater part of the kingdom, 
living side by side, ¢evvestrzs rarely if ever inter- 
breeds with Zucorum, and ruderatus with hortorum, 
for intermediate specimens are seldom found, and 
I have never known both forms to be produced by 
the same queen. In each case there is evidently 
a barrier between the two forms that does not 
exist ; for instance, between the English and Italian 
races of the honey-bee which, when brought to- 
gether, cross freely, and it seems best to regard 
them as distinct but closely-allied species. 
Between a slight differentiation, such as that which 
separates BL. terrestris from LB. lucorum, and the 
deep divisions that part well-marked species, all 
degrees of relationship occur. J. datrezllellus and 
B. distinguendus are almost as closely related to 
one another as ¢Zervestris and Zucorum; the differ- 
ences between L. pratorum, L. jonellus, and B. 
lapponicus are slightly deeper, and those between 
B. derhamellus and LB. sylvarum deeper still: in 
the last case decided differences in the shape of 
the armature appear for the first time. 
In Shetland, large-sized varieties of B. zonellus 
and L. muscorum, having the coat longer and more 
deeply coloured than it is in the mainland forms, 
