MURID^ 375 



material. The cortical portion supplied by the female is com- 

 posed of detached epidermical cells. Gestation lasts normally 

 thirteen to twenty-two days ; but if the female is already rearing 

 a litter, the development of the embryos may be suspended, 

 their birth being postponed for another ten to fourteen (total, 

 twenty-three to thirty-six) days. Pairing may take place very 

 shortly after parturition. Lactation lasts roughly until the eyes 

 of the young open, that is, about eleven days. The young 

 of all British species are born naked, with a pink skin, 

 blind, and with closed ears, but grow with much rapidity. If 

 disturbed suddenly in the nursery the mother rushes out with 

 her babies attached to her teats, but they soon drop off, and, 

 if allowed to do so, she will carry them home in her mouth, 

 her more usual method of handling them (see Lataste, 

 Marshall, etc.). 



Longevity:— Little is known on this point, and the general 

 statement of Metchnikoff ( 7"^^ Prolongation of Life, 1907, 57), 

 that the limit is five or six years, is probably not far from the 

 truth. No member of the family has reached seven years in 

 the London Zoological Society's Gardens (Mitchell). 



History (including Muscardinus) : — Accurate knowledge of 

 the distinctions between the various species of rats and mice 

 is of quite recent growth. The older naturalists seem to 

 have confused shrews and mice, and Linnaeus's genus Mus 

 embraced twenty-two rodents now assigned to almost as many 

 genera. Amongst British authors, Merrett in 1666 mentioned 

 five species, only four of which are rodents : " the house 

 Mouse," "a Rat," "a Water Rat," "the Erdshrew or Field 

 Mouse," and "a Sleeper or Dormouse." Ray (1693) rightly 

 separated the mice from the shrews, which latter he called 

 Mus araneus ; he added the Field Mouse. Seventy years later 

 Pennant (ist ed., 1766) knew of only two additional species, the 

 Norway Rat and the "Short-tailed Field Mouse." Correct 

 technical names first appear in Berkenhout (1769), who used a 

 single genus Mus for the above seven rodents, together with the 

 Harvest Mouse which he added to the list. In Turton (1807) 

 the Dormouse is transferred to the genus Myoxus, all the other 

 species remaining in Mus, a classification which long prevailed, 

 but in 1828 Fleming adopted the genus Arvicola for his Field 



