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FOUR FIGURESI n a recent paper on the influence of temperature, food supply, sex and age on the rate of growth of this species, it was shown that on the coast of Southern California the mu+ sel under favorable conditions may reach a length of 80 to 86 mm. at the age of 1 year, 120 mm. when 2 years old and approximately 145 mm. at the end of the third year (Coe and Fox, '42). The habitat, food, digestion and salinity require- It now remains to consider some of the substances of which the body and shell of the mussel are composed, the amounts and sources of the materials which have contributed to the growth of the tissues and the deposition of the shell as well as the various ways in which the metabolism of the mussel affeds the associated organisms in the vicinity.

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.