592 Life-histories of Northern Animals 



The foregoing refers to their summer and breeding nests. 

 The winter or sleeping nest is in the ground, two or three feet 

 from the surface, and is thoroughly warmed and lined with 

 leaves and grass. 



MATING All the evidence available goes to show that this species 



pairs. Whenever a nest is found in winter it contains either 

 one or a pair. Bailey records^ that in July, 1887, at Harwood, 

 Dakota, he found two in a nest near a wheat-field. Preble 

 found Zapus montanus nesting at Crater Lake, Oregon, 

 August 18, 1896,^ and says^ of these elaborate late summer 

 structures: "These nests are usually occupied by two indi- 

 viduals, presumably a pair, and seem to be used only at the 

 close of the breeding season." 



On September 8, 1903, while camped in the Bitter Root 

 Mountains of Idaho, the cook brought me a male Jumping- 

 mouse (Z. princeps) caught near by. Its sexual organs were 

 much enlarged and had all the appearance of rut. It is 

 possible that, like several other hibernators, the species mates 

 in the fall. 



BREED- As already noted, Preble collected a number of Hudsonian 



Jumping-mice between Lake Winnipeg and Hudson's Bay. 

 He found in them from 5 to 8 embryos. The following details 

 have been supplied me from his note-book: 



*' Robinson Portage, June 28, 1900. Two specimens, 5 

 and 6 embryos, respectively; of 20 adult specimens taken at 

 Oxford House, 5 were adult females, which were fully examined 

 and then entered: June 30, i with 5 embryos; July i, i with 

 8 embryos; July 2, 3 with 6, 7 and 8 embryos, respectively." 

 As no young were taken, this shows conclusively that the 

 latter are produced in July in that latitude. It is well to remem- 

 ber here a principle elsewhere laid down, that the young in the 

 nursery average lower in number than uterine embryos. Most 

 hen's nests have some eggs that come to nothing. Kennicott 



' Rep. Cm. U. S. Dep. Agr., 1888, p. 447. * N. A. Fauna, No. 15, 1899, p. 29. 

 Ubid., p. 8. 



ING 



