O.rborn Zoological Lubol-atory, r a l e iYniversity TW'BNTY-TIIRPE FIGX-RES ACTIIORS' AllSTRACTThe clam Mys differs from other pdccypods which have been investigated in this respect in having most of the reserve nutritive materials formed within the varuolated follicle cells of the gonads instead of within the very limited amount of mesenchymatous connective tissue of tlitt viseeritl mass. The profuarly brsnrhing tu1)uin.r gonads nriginabo from two groups of primordial germ cclls situatcd in tho position of the future gcnital apertures. The germinal prirnordia soon hncomc diffcrantiated into two types of nuclei one of which hecomes associated with the large, vacuolnted follicle wlls, which form the princjpal vtrlume of the gonadal tissue, while the other type proliferates to form the primary gonia which bccotne widely scattrred along the walls of each alveolus.Thwo is niueli rlagei1er;ition and cytolysis during gnmetogenesis in both sexes, with the accumultilion of vhnrncterifitic inclusions within the follirle cells. Atypical spermatogenesis followcd by cytolSijis oc('urs throughout the year but the normal method only in preparation for spawning. No evidence of protsndry or change of sex was obtained; only three 1irrm:iphroditeu wrrt? f o u n d in the rx:iinination of inore thaii 1000 individuals.During the past few years it has been found that in several species of pelccypods all or nearly all individuals are protnndric, with a strong tendency toward alternating female and male phases in later lifc. In the viviparous oysters (Coe, '34; Orton, '36) and in at least one species of Teredo (Coe, '36) there may be two or more of these funct.iona1 phases within a single year. In the oviparous oysters the dominance of protandry is less complete, the proportion of individuals functioning as females during their first breeding season dcpending upon the locality and the environmental conditions. In older individuals the sexual phase may change in the interval betimen two breeding seasons or even dulaing R single breeding season in the case of young individuals under certain conditions (Coc, '36 a ) . In the quohog, on the other hand, an initial male phase leads to either of the unisexual phases, with no evidence of a second change of sex (Loosanoff, '36, '37). 91JOURKAL OF MORPHOMGY, VOL. 62, NO.

The behavior of the beach clam, Donax variabilis, resembles that of Donax semigranosis in that it migrates up and down the beach with the rise and fall of the tide assisted by the wash of the surf. On the rising tide the acoustic shock of the breaking waves stimulates the bivalve to emerge from the sand in advance of the uprush so that the wash carries it up the beach. On the falling tide it ignores the acoustic stimulus and emerges into the backwash to be carried down the beach. The reactions may be due to an intrinsic rhythm, changes in the water content of the sand, or a trigger‐and‐memory mechanism.

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relation passes through it and the pure azeotropic agent point, provided there , is no association, in which case two points must be known. Consequently, the search for the best azeotropic agent for the separation of the constituents of a mixture is simplified and made less time-consuming.