All the females taken were examined for embryos, and the results are here tabulated by species and dates. The term _subadult_ is used to indicate an individual which has reached adult size, but which is still immature as shown by the pelage, unworn condition of the teeth, and weakness of the skull sutures. For each individual the age is first stated, next the number of embryos if any, and last the length of the embryos in millimeters measured as they lie rolled in the fetal membranes. For embryos too small to measure with field equipment the term _small_ is applied. These records indicate the breeding period of the different species and the number of young. _Mephitis nigra._ Eastern skunk August 19: subadult, 0 embryos. _Peromyscus leucopus noveboracensis._ Northern white-footed mouse July 16: adult, 3 embryos, size small. July 21: adult, 0; adult, 0. July 22: adult, 5, 10 5 mm.; subadult, 0. July 23: subadult, 0. July 25: juvenile, 0, juvenile, 0; juvenile 0; subadult, 3, small. July 30: adult, 0; adult, 0; adult, 0; subadult, 0. August 2: adult, 0; subadult, 2, small; subadult, 0; subadult, 0. August 5: adult, 5, small; subadult, 0. August 23: subadult, 0; adult, 5, 10 mm. August 24: adult, 5, 8 mm.; adult, 0; adult, 0; adult, 3, small. August 25: adult, 5, 23 mm.; adult, 0; adult, 4, small; adult, 3, small. August 26: subadult, 4, 8 mm.; adult, 0. August 29: adult, 4, 17 mm. _Peromyscus maniculatus bairdii._ Prairie white-footed mouse August 7: subadult, 0. August 10: adult, 5, 8 mm. August 13: adult, 3, 8 mm.; adult, 0. August 20: adult, 5, small. August 28: adult, 4, 17 mm.; adult, 4, 13 mm. August 29: adult, 5, 17 mm. August 30: adult, 0; adult, 4, 11 mm. _Synaptomys cooperi._ Cooper lemming-vole August 11: adult, 2, 10 mm. _Microtus pennsylvanicus pennsylvanicus._ Pennsylvania vole July 15: adult, 4, not measured, juvenile, 0. August 9: subadult, 0. August 10: subadult, 0; subadult, 0. August 13: subadult, 0. August 16: adult, 0. August 24: adult, 4, 11 mm. _Microtus ochrogaster._ Prairie vole July 25: juvenile, 0. August 15: adult, 4, small. _Microtus pinetorum scalopsoides._ Northern pine vole July 22: juvenile, 0. July 25: juvenile, 0. July 31: adult, 0. _Rattus norvegicus._ Norway rat July 11: adult, 7, 37 mm. July 12: adult, 9, 26 mm. July 14: juvenile, 0. _Mus musculus musculus._ House mouse July 9: subadult, 0. July 10: juvenile, 0; subadult, 0. July 11: adult, 0 (was nursing 3 or more half-grown young). July 17: adult, 11, 6 mm. July 22: adult, 7, 3.5 mm. _Zapus hudsonius hudsonius._ Hudson Bay jumping mouse July 27: subadult, 0. _Marmota monax monax._ Southern woodchuck July 11: adult, 0. July 28: juvenile, 0. August 3: adult, 0. August 22: juvenile, 0.