1906. Moffat. — The St? ugglcfor Existence. 1 03 
we must remember that it suffices to keep an animal down by 
the law of competition, if food or some other necessary is 
scarce for a part of the year, or at some given stage, it may 
be only a short stage, in the term of the animal's life. For 
example, I think the frog, however much it is preyed on by 
enemies, is as common in Ireland as it could possibly be. 
There may be plenty of feeding-ground for more frogs ; but 
are theie any additional nurseries, or any more accommoda- 
tion in existing nurseries, for more tadpoles ? It seems to me 
that every spring the maximum quantity of frog-spawn that 
all the shallow ditches and suitable bog-pools can hold is 
deposited in those places. A great many of these pools dry 
up, as often as not before any of the tadpoles are able to live 
out of the water, and even among the pools that don't dry 
altogether, a great many shrink so much that the poor tad- 
poles find themselves inhabiting a sort of Black Hole of 
Calcutta, and very few of them live to become frogs. But 
allowing that they all became frogs, it still stands to reason 
that no greater number can be reared the next year or the 
next year, because there is no room for more spawn. This 
may keep the number of frogs, as I have before suggested 
that competition for breeding-grounds may keep the number 
of birds, permanently fixed at a number possibly somewhat 
smaller than that which could find subsistence in the country. 
So, when we talk of a fully crowded world, it does not follow 
that every or indeed any species of animal, during the greater 
part of its life, is so numerous as to endanger either the 
permanence of its food supply or the maintenance of its 
health. 
But that many animals live near this high-water mark we 
also have ample proof. When we look to cases like that of the 
vole-plague, which occasionally devastates neighbouring 
countries — for example, the great vole-plague that occurred in 
Scotland in 1892, and the accounts of which made us all feel 
thankful for the complete absence of voles from the Irish 
fauna — we find that though hawks and owls and buzzards and 
weasels and stoats and foxes invariably multiply round the 
affected area and prey extensively on the voles, it is not to 
their efforts that the creatures succumb in the end. The voles 
apparently go on multiplying till their numbers produce 
