BULLETIN OF THE BUREAU OF FISHERIES. physical conditions of the waters in which different species thrive and attain their maximum growth, food supply, enemies and diseases, rate of growth and the influence of environmental factors upon it, and the behavior of glochidia and fishes as parasites and hosts, respectively. * * * I have, however, observed on several occasions a violent and sudden reversion of the water currents such as would certainly be fully capable of carrying the eggs forward and into the latticed recesses of the outer gills. This reversion is caused by the animal, firstly, closing all the ventral border of the shell by means of the free edges of the mantle assisted by the flexible, uncalcified rim of periostracum and leaving the siphons alone open, and, secondly, relaxing the adductor muscles so as to allow the elastic ligament to make the valves gape apart. These actions cause the hydrostatic pressure within the shell to be less than that of the water without and consequently there ensues a rush of water into the shell through the open siphons. The whole procedure may be likened to a gulp and is achieved by precisely similar physical forces.

N their pursuit of better things for better living, many animals have evolved Iefficient reproductive accessories that enable the female to store for long periods of time spermatozoa received from the male. In insects generally, and in Drosophila melanogaster in particular, the sperm-storage organs, of which there are two kinds, are peculiar structures whose modus operandi is not immediately apparent from direct inspection. Not only are the sperm-storage organs, the ventral receptacle and the spermathecae, highly specialized, but the sperm themselves are extraordinary structures, attaining in D. mekmogmter a length of

EXPLANATION OF FIGURES Gravid female of Ptychobranchus phaseolus. X 2Gravid female of Lampsilis subrostratus. Natural size.Gravid female of Obliquaria reflexa. Natural size.Gravid female of Quadrula ebena. X +.Gravid female of Lampsilis rectus. X 3.Gravid female of Symphynot,a complanata. X i.

An EMS-induced, sex-linked recessive lethal mutation that in heterozygous condition mimics the third-chromosome dominant mutant Ultrabithorax-130 (Ubx130) has been discovered in Drosophila melanogaster. This Ultrabithorax-like (Ubl) mutant, when heterozygous, adds several hairs to and enlarges the apical segment (capitellum) of the haltere. Ubl fails to complement Ubln [previously called l (1) L5], a recessive lethal null allele located in section 10C of Bridges' (1938) map of the polytene X chromosome at map position 35.7 Ubl behaves as an antimorph: heterozygous deficiencies for section 10C do not display the Ubl dominant phenotype. Ubl shows a dosage effect: the maximum expression occurs in females with the genotype Ubl/Ubl; Dp Ubl+, in which the capitellum is about three times as large as that of Ubl/+, with two or more rows of bristles. These flies are poorly viable and sterile when mated to Ubl; Dp Ubl+ males, but produce a few offspring when mated to Ubl+ males. Ubl displays a complex series of interactions with loci other than Ubx and elicits expression of specific mutant phenotypes when it is heterozygous in trans with certain nonallelic deficiencies and recessive mutations. Greenleaf et al. (1980) have demonstrated thatUbl is allelic with an alpha-amanitin-resistant mutation that effects RNA polymerase II; therefore, the interactions observed between Ubl and other loci may result from an inability of heterozygous Ubl flies to undergo normal transcription.

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