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. Xo 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 Epei'roids 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 



Power to elevation in their distribution. But the facts concerning them 



Resist 



-g . all 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 ii m i te d to the southern belt of States; and although in geologi- 

 Distribu- ca ^ time > as ear ly at least as the oligpcene or the tertiary, the 

 tion. 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 

 acantha wn i n 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 



