Societies and Academies

Abstract

LONDON. Challenger Society, October 28.—Mr. A. E. Shipley, F.R.S., in the chair.—Ostracoda of the Bay of Biscay captured during the 1900 cruise of H.M.S. Research: Dr. G. H. Fowler. More than 7000 specimens had been identified, and in the case of more than 3000 the sex had been determined and the length of the shell measured. As the result of these measurements the author was enabled to formulate provisionally a new law of growth in Crustacea:—“during early growth each stage increases at each moult by a fixed percentage of its length which is constant for the species and sex”; for this the name of Brooks's law was suggested, Prof. W. K. Brooks having made the first observations which led to it; it had been checked to some extent by observations on lobsters (Herrick) and crabs (Waddington). In several cases it was shown that two stages of the same species had been described as different species. Twenty-five species occurred in the collection, and in some cases as many as five stages had been recognised. As regards the vertical distribution, attention was directed to an increase in the number of specimens captured between 750–400 fathoms as compared with those from 400–100 fathoms, and the suggestion made that this was due to a check in the velocity of fall of dead and dying specimens, produced by the increased viscosity of the water, which in its turn was dependent on increased pressure and diminished temperature. All the four plentiful species, which were recognised on other grounds as mesoplanktonic, attained their maximum intensity in this zone, which would constitute a rich food-zone. Three species were apparently purely mesoplanktonic; eleven reached their maximum intensity in or near the epiplankton, but extended into the mesoplankton, and of these eleven three were apparently purely mesoplanktonic at their oldest stage; four were purely mesoplanktonic. The question of the vertical oscillation of the species was discussed, and several were shown to be more abundant in the epiplankton by night than by day; in one case an attempt was made to trace the movement of the species at different times of day. The proportion of males to females seemed to point to the probability that one species was parthenogenetic. In another species the death-rate at three stages was worked out, and appeared to be 50 per cent. Except in one case the maximum intensity of closely similar species appeared to be at different levels.