ON THE EFFECT OF REMOVAL OF THE LITTER UPON THE REPRODUCTIVE RATE OF THE FEMALE MOUSE

¹ Animal Breeding Research Department, Edinburgh University

The reproductive phase of the sex cycle consists of two periods separated by an strous phase: the first of these periods is occupied by pregnancy, the second takes the form either of lactation or else of another pregnancv. Pregnancy and lactation are of equal duration and are alternative events, and so the reproductive phase represents a double pregnancy period. In any description of the reproductive phase the lactation period must be distinguished from the period of pregnancy. The non-suckling fematle can give birth to twice as many offspring in a given period of tiime as can the suckling.