22 FOOT-NOTES TO EVOLUTION. 
ver, as other bees can not reach the nectar. .. . Hence 
we may infer as highly probable that, if the whole genus 
of humble-bees became extinct or very rare in England, 
the heartease and red clover would become very rare 
or wholly disappear. The number of humble-bees in 
any district depends in a great measure on the number 
of field mice, which destroy their combs and nests; and 
Col. Newman, who has long attended to the habits of 
humble-bees, believes that more than two thirds of them 
are thus destroyed all over England. Now the number 
of mice is largely dependent, as every one knows, on the 
number of cats; and Col. Newman says, ‘ Near villages and 
small towns I have found the nests of humble-bees more 
numerous than elsewhere, which I attribute to the num- 
ber of cats that destroy the mice.’ Hence it is quite 
credible that the presence of feline animals in large 
numbers in a district might determine, through the in- 
tervention first of mice and then of bees, the frequency 
of certain flowers in that district.” 
Huxley carries this calculation still further by show- 
ing that the number of cats is dependent on the number 
of unmarried women. On the other 
hand, clover produces beef, and beef 
strength. Thus in a degree the prowess 
of England is related to the number of 
spinsters in its rural districts. This statement would be 
true in all seriousness were it not that so many other ele- 
ments come into the calculation. But whether true or 
not, it illustrates the way in which causes and effects in 
biology become intertangled. 
The calculation has been lately made by Prof. Rufus 
L. Green that at the normal rate of increase from a pair 
of English sparrows, if none were to die except of old 
age, it would take but twenty years to give one sparrow 
to every square inch in the State of Indiana. But such 
Relation of cats. 
to England’s 
greatness. 
