131 
ON THE ORIGIN OF THE ARANEIDAL FAUNA 
OF YORKSHIRE. 
WM. FALCONER, 
Slaithwaite, Huddersfield. 
(Continued from page rr4). 
It is now generally recognised that there is a close connection 
between the geological formation of a district (in its varied 
characteristics of soil, elevation, aspect and humidity), and its 
vegetation. The latter in its turn influences the insect life, 
which is the main source of the food supply of spiders. It is 
certain, therefore, that one of them cannot be affected without 
disturbing the others. This is only in accordance with what 
has frequently been observed, the various forms of life, both 
animal and vegetable, even those the most dissimilar, being 
apparently in some way dependent on each other. Darwin’s 
illustration of the connection between old maids and their 
cats and the fertilisation of clover discloses some unexpected 
relations, while the introduction of goats into St. Helena caused 
in the course of 220 years the total destruction of the woods 
there and led, by the consequent loss of food and shelter, to the 
extinction of several small animals, birds, molluscs and a 
multitude of insects (‘ Voyage of the Beagle,’ Chapter XX1.). 
In other places, cattle, by ‘wholly preventing the growth of 
trees, have excluded from extensive districts not only the small 
animals of every description which subsist on roots, leaves, 
fruits or seeds, and the insects which are dependent on trees, 
but also the birds and other creatures which prey upon insects. 
Field naturalists are often puzzled to account for the fact that 
a species may be abundant in one district and yet absent from, 
or very rare in a neighbouring one, where to every appearance 
the same conditions obtain, and are driven to conclude that 
some slight difference of climate, food, number of enemies, 
etc., which they cannot discern, is the determining cause, 
Other instances might be adduced but sufficient has been said 
to show that any modification which tends to increase, diminish 
or exterminate one element is merely the beginning of a series of 
far-reaching consequences which affect favourably or adversely 
all the Sie organisms in contact, thus introducing a factor 
which so disturbs all existing arrangements that centuries must 
elapse before the balance can be restored. 
In every area at the present day there is, as a result of this 
cumulative and combined effect of all the influences of every 
kind and degree brought to bear upon organisms in the past, 
a general intermingling of types. As regards spiders they have 
* Dr, Wallace, ‘The Geographical Distribution of Animals.’ 
1913 Mar. re 
