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.
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.
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