STRUCTURE AND ECONOMY. OF SPIDERS. 301 
sive. As the globules, therefore, and the line on 
which they are disposed differ so essentially from 
each other and from the rest of the snare, it is 
reasonable to infer that the physical constitution of 
these several portions of the net must be dissimilar. 
The silk of which the cocoons and cells of many 
spiders are constructed also differs remarkably in 
strength and colour from that which enters into the - 
composition of their snares. 
When exposed to the desiccating influence of the 
sun, and of air briskly agitated, the nets of Geometric 
Spiders speedily lose their adhesive property; but 
when formed in situations from which light is ex- 
cluded, and where the atmosphere is not liable to be 
perceptibly disturbed, I have known them retain 
their viscidity for a long period. In a net of Epeira 
diadema constructed in a glass jar, which was placed 
in a dark closet, where the temperature was not sub- 
ject to great or sudden fluctuations, the globules pre- 
served their adhesive power, almost unimpaired, and 
the Jast formed spiral line its elasticity, for more than 
seven months. 
The belief that spiders are incapable of ascending 
the perpendicular surfaces of polished bodies without 
the assistance of lines emitted from their spinners is 
so widely extended, that an attempt to prove its 
fallacy in particular cases will, in all probability, be 
received with some distrust: nevertheless the fact 
that many species have the power of traversing vertical 
