The life-cycle of cladocera, with remarks on the physiology of growth and reproduction in crustacea

In a paper on the life-cycle ofMoina rectirosiris , published in 1913 (5), it was shown by the late Mr. G. H. Grosvenor and myself that it was possible to inhibit entirely the production of the sexual forms by isolating the parthenogenetic parents soon after birth, and keeping them at a constant high temperature of 25-30° C. It was proved that for a succession of eight generations the isolated parents at this temperature gave no males or ephippial females, while parents of the same generations kept crowded at a temperature of about 14° C. or 5° C. gave about 50 per cent, males. We were unable to determine how the effect of isolation and crowding of the parthenogenetic parents influenced the production of the sexual forms, but two alternative suggestions were made, either that in the crowded glasses the animals were unable to obtain sufficient nutriment and were partially starved, or else that some excretory matter accumulated in the crowded glasses which influenced the production of males and sexual females. In order to confirm the above results and to throw some light on the processes involved, breeding experiments have been carried on for some time with another species of Claclocera, the commonDaphnia pulex. Mr. Robert Gurney very kindly gave me some dried mud from a pond winch was known to contain the resting eggs of these animals, and, on placing the mud in a bowl of water, after some weeks some young Daphnia hatched out. One of these was kept until it had produced young, and the offspring of these young ones were used to start the first experimental generation.