ON THE ABILITY OF CERTAIN MARINE INVERTE-BRATES TO LIVE IN DILUTED SEA WATER. A. S. PEARSE, DUKE UNIVERSITY. There are many reasons for believing that animal life originated in the ocean and has gradually spread through the ages into freshwater and land habitats (15, 21). In the past annelid worms invaded the soil, probably by a rather indirect route which led them first into freshwater and gradually out into the land (23). At the present time many animals in various parts of the earth show varying degrees of ability to live in diluted sea water (i, 3, 10, u, 12, 21). Marine invertebrates which have been studied have an osmotic pressure in their blood which is approximately equal to that in sea water, but the mineral salts are somewhat less and the pressure is maintained by other substances, largely organic, which are present (i, 8, 9). The skins of various animals differ greatly in ability to control the exchange of chemicals between the body fluids and the surround-ing medium. Adolph (i) studied the exchanges of substances through the skins of annelids and found that there was little resistance to them. The writer felt that it would be of interest to determine the ability of representative marine annelids to live in diluted sea water, and during August 1927 made some observations in the Marine Biological Laboratory at Woods Hole. Thanks are due to Drs. J. A. Dawson and R. Bennitt who made suggestions and helped in the identification of several species. Mr. A. M. Hilton and his staff of collectors also made special efforts to secure materials. Animals were brought in fresh from the field and placed as soon as possible in clean glass finger bowls containing 250 cc. of water. Tubicolous worms were removed from their tubes, except in the case of Hydroides, which was studied both in and out of tubes, and of Cystenides, which was left in its own tubes. 405
BioStor
