Compared with Lumbricillus lineatus the cocoons of Enchytraeus albidus are smaller and contain fewer eggs whilst the egg production per worm is higher and sterility among the eggs lower. The fecundity of E. albidus is greater over a temperature range 1–25d̀ and is not so adversely affected at the higher or lower temperatures as L. lineatus. Incubation in E. albidus is longer than in L. lineatus but the time required for maturation is much shorter, the periods depending upon the temperature. There is a similar relation to temperature as in the case of fecundity, with E. albidus again more tolerant to heat and cold. There is no relation between size and temperature but unlike L. lineatus, growth occurs after maturation in E. albidus and its cocoons (after the first) and their egg content are larger. There is no apparent relation between the setae length and temperature. The temperature relations favour a more rapid increase of E. albidus in the bacteria beds than of L. lineatus but they are well suited to the distribution of the species under natural conditions, E. albidus favouring a terrestrial habitat whereas L. lineatus exists in moister places. Further, they show specific physiological differences distinguishing the two species of worms.