, i ae 
HORIZONTAL SNARES AND DOMED ORBS. 163 
throughout a great part of the northern hemisphere. The spiders of the 
southern temperate regions have not yet been sufficiently studied to enable 
us to decide whether or not this group is represented there. It certainly 
would be a valuable addition to our knowledge could it be known whether 
they are as widely distributed in the southern hemisphere as in the 
northern ; and especially if it could also be determined whether or not the 
peculiar conditions of the torrid zone have prevented distribution of these 
species across that area. No doubt this would throw light, as far as spiders 
are concerned, upon the power of certain species to originate and maintain 
life independently in certain natural geographical areas. 
Among this group of Epeiroids may be named Epeira insularis or E. 
marmorea, Epeira cornuta or E. strix, E. diademata, E. quadrata or E. trifo- 
lium, E. sclopetaria, and E. patagiata. In the case of some of these species 
the records do not show quite as great extremes of climate and 
: elevation in their distribution. But the facts concerning them 
Resist E : : 
Environ. @! contribute to the general conclusion that certain araneads have 
ment, an immense power of resisting the external influences of their 
environment; possess a remarkable elasticity of temperament, 
which allows them to adapt themselves to widely different conditions of 
life. In the midst of all this, so thoroughly fixed are their habits that 
they resist all those centrifugal influences of varying surroundings which 
are supposed to be so potent to overcome the conservative tendencies of 
natural behavior, 
Environment does influence the distribution of some species. The spider 
fauna of the tropical regions when placed alongside of those of the tem- 
perate zones show marked individuality. There are certain groups that 
have found lodging along the warm regions of our Gulf States, throughout 
Texas and Southern California, but have never been able to push their 
way farther to the north. The genus Nephila, for example, is 
Climate Jimited to the southern belt of States; and although in geologi- 
Limits : : : 
Distribu. ©#! time, as early at least as the oligocene or the tertiary, the 
on genus was established as far north as Colorado, in the region of 
Florissant and South Park, it is not now found above the par- 
allel of Charleston, which in a general way indicates the limit of its north- 
ern distribution. What are the influences that prevent it from breaking 
through this barrier? One must hesitate to answer; but they are prob- 
ably climatic, inasmuch as the genus has immense development in various 
species throughout tropical regions. 
Another example is the genus Gasteracantha or Crab spider, distin- 
guished by its round or circular abdomen, upon the margins of 
which are fixed various spinous processes. (See Chapter VII.) 
In this most striking characteristic, namely, the presence of spines 
upon a leathery abdomen, Gasteracantha certainly resembles the genus 
Acrosoma ; yet that genus has several representatives in our northern spider 
Power to 
Gaster- 
acantha. 
