ON THE MORPHOLOGY OF THE NEPHRIDIUM OF NEREIS VEXILLOSA GRUBE T MEREDITH L. JONES /'r/ 1 /. of Zoolof/v. ['nh'crsitv of California, Berkeley, California 2 It has been well established that certain of the Nereidae are capable of surviving in waters of low salinity. In the field this is demonstrated by their invasion of brackish and even fresh waters (Johnson, 1903; Hartman, 1938; Smith, 1950, 1953, 1956), and has also been suggested in the experimental work of some investigators (Schlieper, 1929; Nomura, 1930; Jurgens, 1935; Sayles, 1935; Beadle, 1937; Ellis, 1937; Topping and Fuller. 1942; Krishnan, 1952; Smith, 1955). In spite of the fact that many physiological studies have been carried out on various nereids, only a few morphological descriptions of the presumed osmoregulatory organ of these annelids, the nephridium, are to be found in the literature. The first detailed description of nephridial morphology was made by Goodrich (1893) on A T crcis dircrsicolor. He found three sections along the length of the nephridial tubule, each grading into the next. The sections varied in respect to the presence or absence of cilia, the diameter of the tubule lumen, and the extent of convolution of the tubule. Fage (1906) studied Pcrincrcis cultrijcra, confining his work to living material. He also found areas of ciliation, but these differed from those observed by Goodrich in X . dirersicolor. Much later, in his extensive review of observations of nephridia and genital ducts, Goodrich ( 1945) re-stated his earlier findings but added little to them. In his work on Lycastis indica. Nereis chilkacnsis, and Perinereis nitntia, Krishnan (1952) made a study of the nephridia of each species and compared them with respect to vascularization and size, relative to body size^ Because of the paucity of adequate morphological studies on nereid nephridia, it was felt that further study was in order, to provide a better basis for physiological work, and for later studies of comparative functional morphology. MATERIALS AND METHODS Specimens of Nereis t'e.rillosa utilized in this study were obtained from a break-water at the Berkeley Yacht Harbor, in San Francisco Bay, California. Although no salinity determinations were made at this time, the annual salinity range for this area is from 26.3 to 32.4/^r (approximately 73 to 90% sea water), according to Sumner ct al. ( 1914) and Miller ct al ( 1928). The worms were relaxed by gradual addition of 30% ethyl alcohol, fixed in Benin's fixative and serially sectioned at eight micra. They were then stained with 1 Representing a portion of a thesis submitted in partial satisfaction for the degree of Master of Arts in Zoology at the University of California at Berkeley. -Present address : United States Naval Mine Defense Laboratory, Panama City, Florida. 407
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