THE RESPIRATORY FUNCTION OF THE BLOOD OF (JRECHIS CAUPO ALFRED C. REDFIELD AND MARCEL FLORKIN 1 (From the Hopkins Marine Station, Pacific Grorc, California) Ureclus caupo is an echiuroid worm inhabiting sandy mud flats in the estuaries of the coast of California. Its characters and habits have been described by Fisher and MacGinitie (1928). Because of its large size, the simple nature of its circulatory and respiratory systems, and the fact that its ccelomic fluid is voluminous and contains abundant red blood corpuscles, it affords unusually suitable material for the study of respiratory problems. The present paper contains a description of those properties of the blood of Urcchis which are of importance in respira-tion, together with certain observations designed to evaluate the sig-nificance of these properties. The material used for these studies was collected in the Elkhorn Slough, a tributary of Monterey Bay. The authors wish to express their indebtedness to Dr. MacGinitie for assistance in procuring the animals and to Professor Fisher for the many courtesies received while they were at the Hopkins Marine Station. I. THE BLOOD OF URECHIS Fisher and MacGinitie (1928) state that the ccelom is filled with bright red blood, the pigment being lodged in subcircular cells, about 0.025 mm. in diameter, which readily distort when crowded. There are also very numerous amoeboid cells which when aggregated are yellow in color. We have found the color of the blood to vary, being frequently of a dull brownish-red color; less often, and particularly in smaller specimens, of a bright scarlet resembling the blood of vertebrates. A volume of 15 or 20 cc. may be secured from a single specimen. The Blood The plasma does not clot, and when separated from the cells is a pale yellow color ; not infrequently it may be tinged with the corpuscular pigment. Under microscopic examination the cytoplasm of the cor-puscles appears yellow and is seen to be filled with small, highly refrac-tive granules. In addition, there are many granules of a brown pigment 1 Fellow of the C. R. B. Educational Foundation. 185
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