GROWTH, SIZE AND REPRODUCTION IN <i>DAPHNIA</i> (CRUSTACEA: CLADOCERA)*

<jats:p> <jats:list list-type="explicit-label"> <jats:list-item><jats:p>Factors influencing the growth of <jats:italic>Daphnia</jats:italic> are summarized; it is shown that lack of oxygen inhibits the growth of <jats:italic>Daphnia magna.</jats:italic></jats:p></jats:list-item> <jats:list-item><jats:p>Synchronization of egg laying by females in samples from natural populations has been found on several occasions.</jats:p></jats:list-item> <jats:list-item><jats:p>The pre‐adult growth of <jats:italic>Daphnia</jats:italic> has been studied by rearing 207 specimens belonging to eight species in standard conditions. The greatest growth increment does not always occur at the end of the adolescent instar; it may occur at the end of the pre‐adolescent instar or more rarely even earlier.</jats:p></jats:list-item> <jats:list-item><jats:p>Initial size influences the instar in which maturity is reached; as the initial size increases the animals tend to become mature in earlier instars.</jats:p></jats:list-item> <jats:list-item><jats:p>In single samples from natural populations a direct correlation has been found between the size of the females and the number of eggs carried in their brood pouches. This applies to several species of <jats:italic>Daphnia</jats:italic> and certainother Cladocera (excluding the subfamily Chydorinae).</jats:p></jats:list-item> <jats:list-item><jats:p>Synchronous fluctuations in the size of parthenogenetic females and the number of eggs in their brood pouches have been found in a population of <jats:italic>D. magna.</jats:italic></jats:p></jats:list-item> <jats:list-item><jats:p>Factors influencing the size of eggs and young are analysed. Within a species the following factors are operative: egg number in relation to the size of the mother, the age of the mother, inherited racial or clonal characteristics, available food and temperature.</jats:p></jats:list-item> <jats:list-item><jats:p>The size of the ephippial eggs of <jats:italic>D. magna</jats:italic> varies with the size of the female producing them. The ephippial eggs may be bigger or smaller than the parthenogenetic eggs.</jats:p></jats:list-item> <jats:list-item><jats:p>The eggs of thirty‐three species of Cladocera have been measured. The larger species produce eggs which are slightly larger in relation to maternal size than those of the smaller species.</jats:p></jats:list-item> <jats:list-item><jats:p>A mature female of <jats:italic>D. magna</jats:italic> can assimilate enough material during each instar to produce eggs with a dry weight at least equal to that of her body after the eggs have been laid.</jats:p></jats:list-item> <jats:list-item><jats:p>The dry weight of the parthenogenetic egg of <jats:italic>D. magna</jats:italic> diminishes by 16 to 25 per cent during embryonic development.</jats:p></jats:list-item> </jats:list> </jats:p>