RELATION OF THE RATE OF ANTENNAL MOVEMENT IN DAPHNIA TO THE NUMBER OF EGGS CARRIED IN THE BROOD POUCH

The number of parthenogenetic eggs and embryos carried in the brood pouch of Daphnia varies greatly. In some natural populations of the pond-dwelling species females carry many eggs, * in other populations they have few. We have found in nature a female of D. magna Straus carrying 95 eggs, and de Kerherve (1926) had one in culture with 105 eggs, whilst, on the other hand, in some natural populations of the same species no more than one, two or three eggs are borne. Two potent causal factors influencing egg number are the quantity of food and the aeration of the water: up to a certain maximum level of feeding, the number of eggs produced is proportional to the quantity of food eaten (Ingle, Wood & Banta, 1937; Fox, Hardcastle & Dresel, 1949), and below a certain degree of aeration of the water the egg number falls off proportionately to the amount of dissolved oxygen (Fox, Gilchrist & Phear, 1951). In addition, fewer eggs are produced at a high tempera