ANDRENA. * 207 



former depending upon both the quantity and quality 

 of the food stored up, for the pollen of different plants 

 varies possibly in its amount of nutriment, else why 

 should we observe so marked a difference in the sizes 

 of individuals whose parent instinct would prompt to 

 furnish them with an uniform and equal supply. The 

 differences of specific appearance is often very consider- 

 able in long genera, and perhaps in no genus is it 

 more conspicuously so than in Andrena, for here we 

 have some wholly covered with dense hair, and others 

 almost glabrous; others again with the thorax only 

 pubescent ; some are black, some white, some fulvous, 

 or golden tinted, and some red; some we find banded 

 with decumbent down, and others with merely lateral 

 spots of this close hair, but the most prevalent colour 

 is brown, which will sometimes by immaturity take a 

 fulvous or reddish hue. In many males we see excen- 

 trically large transversely square heads broader than the 

 thorax, which also have widely spreading forcipate man- 

 dibles, with often a downward projecting spine at their 

 base beneath; and it is chiefly these extravagantly 

 formed males which are most dissimilar to their own 

 partners that the result of observation alone confirms 

 their specific identity. In other cases the males are so 

 like their females that a mere neophyte would unite them. 

 In many males the clypeus and labrum are white, which 

 also occurs in some females ; for instance, in A. labialis, 

 but this peculiarity is found more rarely in this sex. 

 The species are much exposed to the restricting in- 

 fluences of several parasites, whose parasitism is of a 

 varying character, but the term should properly be ap- 

 plied only to the bees which deposit their eggs in their 

 nests, and whose young, like that of the cuckoo among 



