•J BIOLOGICAL SOCIETY OF WASHINGTON. 



ialists on such voyages as those of the British vessels, Lightning, 

 Porcupine, Valorous and Challenger; the French Talisman, and 

 Travilleur; the Norwegian, North Atlantic Expedition ; and 

 the explorations of our own Coast Survey, Fish Commission, 

 and Navy on the Blake, the Fish Hawk, the Albatross, and 

 other well known vessels. The most distinguished naturalists 

 of this country and of Europe have added to their reputation 

 by the investigation of the wonderful fauna revealed by these 

 explorations. The most extensive and important single series 

 of Scientific Reports ever published as the result of a single 

 expedition are those which bear the name of the Challenger 

 upon their capacious covers. Next to these come the Reports 

 of the United States Fish Commission, under the leadership of 

 Prof. Baird, and then follows a host of minor documents which 

 it is impossible to enumerate at the present time. 



What I have to present to you this evening is rather a dis- 

 cussion of conditions and principles than an exhibit of particu- 

 lar facts or observations. 



In order that their existence may be maintained the abyssal 

 mollusks require oxygen to aerate their circulation, food to eat r 

 and a foothold upon which they may establish themselves. It 

 is necessary that the conditions should be such as will not pre- 

 vent the development of the eggs by which successive genera- 

 tions are propagated, and that they do permit it may be 

 assumed from the very fact that mollusks in large numbers 

 have been shown beyond all question to exist on the oceanic 

 floor wherever this has been explored. 



Formerly when dredging with the usual appliances in small 

 boats, one hundred fathoms (six hundred feet) was considered 

 extremely deep. If one stands at the foot of the great Wash- 

 ington obelisk and looks up, the idea of collecting a satisfac- 

 tory representation of the insects and plants on the ground at. 



