Origin of the Araneidal Fauna of Yorkshire. E¥3 
so continuously in both the animal and vegetable kingdoms. 
This must have operated also in the case of spiders and helped 
to produce those wonderful modifications of structure and 
modes of life, the one adapted to the other, which have enabled 
them to occupy the most diverse situations, and to become one 
of the most widely diffused animals on the face of the earth. 
While some are not particular what these situations may be, 
the greater number have appropriated to themselves special 
habitats, in the absence of which it would be useless to search for 
them; for example, Tegenaria derhamii Scop. confines itself 
to buildings; Evigone longipalpis Sund. and Halorates re- 
probus Camb. haunt the sea coast ; Drapetisca socialis Sund. 
and Styloctetor penicillatus Westr. frequent tree trunks ; Salticus 
scemicus Clerck searches walls; Evansia merens Camb. is an 
inhabitant of ant’s nests; Tvochosa picta Hahn hunts over 
sandy tracts; Argyroneta aquatica Latr. attaches its bell-like 
retreat to the submerged stems of water plants; Purata 
piraticus Clerck, P. hygrophilus Thor., Dolomedes fimbriatus 
Walck. live in watery places and can on occasion descend 
into the water; Misumena vatia Clerck. lurks in flowers to 
seize their insect visitors. 
Such specialisation amongst spiders is far from being 
exhausted by the examples given above. This same diversity 
of structure and mode of life has in itself a tendency to dissemi- 
nate the species, for the necessity under which these creatures 
are often laid of finding an unoccupied habitat of the kind 
required and in competition with others of enlarging the area 
from which a sufficient supply of food can be drawn must 
constitute an ever present and all powerful incentive to spread. 
To assist them in this dispersal, they have acquired the power, 
extraordinary in creatures unprovided with wings and re- 
markable also for the simple means by which it is apparently 
accomplished, of sailing through the air. No combined move- 
ment is made, but each individual rises and floats away by 
itself. Single floating threads are not easily detected, and it 
is very probable that this habit of aviation is much commoner 
and more widespread among spiders than is usually supposed. 
The intending aeronaut climbs to the top of a post, gate or 
bush, and elevating its abdomen, emits from its spinners a 
long filament on which is is borne rapidly through the air 
to a considerable distance and often at a great height. Most 
naturalists will have at least read the accounts of this phenome- 
non in White’s Selborne Letter XXIII. to Hon. D. Barrington 
and Dr. Lister's De Araneae as given in Kirby and Spence’s 
“ Entomology’ Letter XXIII, but if not can readily turn to 
them. It is difficult to believe, however, that nothing more 
than the filament and the assistance of the wind is needed to 
effect this wonderful flight. Under atmospheric conditions of 
tg13 Feb. 1. 
