268 AMP;KICAN spiders and their SI'lNNINdWOUlC. 



them from the objects to which they were attached, and has raised them 

 into tlie atmosphere. He, liowever, added the opinion that, "as they never 



make use of them intentionally in the porforiiiance of their aero- 



° ^^ nautic expeditions, it must always be regarded as a fortuitous 



looninc' circumstance."' This opinion, I think, must be abandoned, and 



the conclusion reached that there are two modes of ballooning 

 practiced by spiders, viz. : First, ascent by means of the buoyancy of lines 

 issuing directly from the spinnerets, the aranead vaulting ui)ward from 

 its perch ; and, second, the ascent upon lines, sometimes thickened by flossy 

 tufts or strands, which are first spun out and attached to fixed objects, and 

 afterward released by the force of the wind or cut loose by the spider. 



VI. 



While arranging a collection of spiders in the Academy of Natural 



Sciences of Philadelphia, I discovered a number of specimens of a large 



Laterigrade, the Huntsman spider, Pleterapoda venatorius, from 



Aerial various localities, as represented upon the accompanying tables 



ircum- ^^^^^ chart. (Fig. 278.) Starting with the specimens in my private 

 naviga- . ... j i 



tion collection, the line of distribution was traced from Santa Cruz, 



Virgin Isles, to Cuba, to Florida, across Central America, Yucatan, 

 and Mexico; across the Pacific Ocean by way of Sandwich Islands, Jai)an, 

 and Loo-Choo Islands; and thence across the continents of Asia and Africa 

 to Liberia. The line thus indicated extends fi'om the extreme eastern limit 

 of North America to the extreme western coast of Africa, thus girdling the 

 globe, with the exception of 54° of longitude. This excepted area ex- 

 presses substantially the width of the Atlantic Ocean. 



It occurred to me, when this fact became apparent, that this line of 

 distribution is within the belt of the North Trade Winds; and, further, 

 that there might be some connection between the two facts and the fact 

 that Laterigrade spiders, to which group this animal belongs, are among 

 those which are most addicted, in the earlier stages of growth, to balloon 

 migration. Thereupon I referred to the general course and limits of the 

 North Trades, which are roughly indicated in the chart (Fig. 278) by the 

 two upper lines of arrows, marked (at the ends) A A and B B. In the At- 

 lantic Ocean the North Trade Winds prevail between latitude 9° N. and 

 30° N. ; in the Pacific between 9° N. and 2G° N. We now may turn to 

 the chart, in which the following geographical points (shown by black 

 spots and figures) are represented by our spider. The specimens which 

 have been examined in the Academy, and my own collections, whose habi- 

 tats are personally known, are marked by an asterislc (*). 



The species is credited to the other localities named on the authori- 

 ties given therewith. 



' Blackwall, Spiders of (it. Hr. and Ir., Introduction, page 12. 



