160 AMERICAN SPIDERS AND THEIR SPINNINGWORK. 
ning over water, and behavior when cast upon water, I wished to observe. 
The beaten marsh grass yielded me no Dolomedes, but instead several 
half grown Tetragnatha vermiformis, Emerton, dropped upon the surface, 
To my surprise they seemed not the least disconcerted, but immediately 
recovered themselves and with one exception ran to the shore precisely 
as do the Lycosids. The excepted individual had been thrown out from 
the bank farther than its comrades. For a moment it paused, its body 
bowed and held upward upon the eight legs which were spread out so 
that the feet marked the outline of a rude cirele upon the surface. Then 
it started rapidly across the mouth of a tiny baylet between a tongue of 
the land and the main shore, traversed the intervening space, 
and pulled itself to the land by the overhanging grass. My 
attention was attracted by the remarkable fact that during 
this transit there was no appreciable movement of 
the legs. ‘That an Orbweaver should be able to glide 
so rapidly and gracefully over water was a fact 
in itself sufficiently new to me; but that one 
should do this without any physical exertion 
whatever amazed me. Could the action of the 
air upon the body have been the impelling force ? 
I addressed myself eagerly to the solution 
of this mystery. A second clump of grasses 
was beaten, and a Tetragnatha fell upon the 
lake. She ran over the water to the shore, 
using apparently her fore legs as paddles. Be- 
a \ fore she climbed into the grasses I 
> : thrust my cane under her body, 
gently lifted her up, and reaching 
outward as far as I could, gradually 
sunk the tip of the stick into the 
—— water without causing any ruffling 
= Se ke of the surface. The spider was thus 
Tic. 152. Silken sails: Tetragnatha navigating a lake. eased off the stick and place d upon 
the surface undisturbed. As soon as she felt herself fairly launched she 
made a few strokes with her fore feet, then suddenly paused and thrust the 
apex of her abdomen down to the surface. Directly, the abdomen was 
raised from the water and turned up until it made an angle of about 60° 
with the surface. Next a long streamer of silk filaments was emitted from 
the spinnerets, precisely as in the case of aeronautic spiders when about to 
ascend, and immediately the spider began to scud at a great rate over the 
water, The mysterious motor was thus reyealed—the silken threads served as 
sails upon which the wind played, propelling the vital craft across the water. 
The discovery into which I was thus accidentally led was so interesting 
that I devoted the remainder of my day to the full investigation of the habit 
