fTumble-Bees and other Matters. 155 
served them, there has occurred no change in their 
relative positions; though both have greatly in- 
creased in numbers during that time, owing to the 
spread of cultivation. And yet it would scarcely 
be too much to expect some marked change in a 
period so long as that, even through the slow- 
working agency of natural selection; for it is not 
as if there had been an exact balance of power be- 
tween them. In the same period of time I have 
seen several species, once common, almost or quite 
disappear, while others, very low down as to 
numbers, have been exalted to the first rank. In 
insect life especially, these changes have been 
numerous, rapid, and widespread. 
In the district where, as a boy, I chased and 
caught tinamous, and also chased ostriches, but 
failed to catch them, the continued presence of 
our two humble-bees, sucking. the same flowers 
and making their nests in the same situations, has 
remained a puzzle to my mind. 
The site of the nest is usually a shght depression 
in the soil in the shelter of a cardoon bush. The 
bees deepen the hollow by burrowing in the earth; 
and when the spring foliage sheltering it withers 
up, they construct a dome-shaped covering of small 
sticks, thorns, and leaves bitten into extremely 
minute pieces. ‘They sometimes take possession of 
a small hole or cavity in the ground, and save 
themselves the labour of excavation. 
Their architecture closely resembles that of B. 
terrestris. They make rudely-shaped oval honey- 
cells, varying from half an inch to an inch anda 
half in length, the smaller ones being the first 
