604 



THE AMEBIC AN NATUBALIST [Vol.XLVI 



From birth to maturity mice pass through several well- 

 defined stages which to the breeder are of importance for 

 the determination of age, sex and the like. These are 1 

 an early stage in which the skin is peculiarly red so that 

 through it may be seen the stomach white with milk; 2 

 a second stage at six to seven days in which the body is 

 covered with flakes of dandruff ; 3 a stage at nine or ten 

 days in which the mammae appear in the females. This I 

 have designated as the stage for the early determination 

 of sex; 4 on the fourteenth day a stage at which the 

 eyes open. 



At twenty- one days the young should be weaned. From 

 this time on slight change is shown except increase in size 

 until sexual maturity is reached. This usually occurs in 

 the second or third month. From this time up to the end 

 of ten months or a year of age the mouse is in the height 

 of the breeding period ; beyond this time, for purposes of 

 breeding, the mouse is usually of little further service. 



BIBLIOGRAPHY 



1. Cuenot, L. 1902. La loi de Mendel et L 'heredity de la pigmentation 



cbez les souris. Arch, de Zool. Exp. et Gen., 3 e -serie, Tome X (Notes 



2. Ehrlich, P. 1891. Experimented Untersuchungen iiber Immunitat. 



Deutsche med. Wochenschrift, p. 976. 



3. Bashford, E. F. 1909. Cancer in Man and Animals. Lancet, clxxxvii, 



4. Yerkes, Robert M. 1907. The dancing mouse; a study in animal be- 



havior. The Macmillan Company. 



5. Long, J. A. and Mark, E. L. 1911. The Maturation of the Egg of the 



Mouse. Pub. Carnegie Inst. (Washington, D. C), No. 142. 



6. Daniel, J. Frank. 1910. Observations on the Period of Gestation in 



White Mice. Journ. Expt. Zool, IX, p. 865. 



7. Miller, Newton. 1911. Reproduction in the Brown Rat. AM. Nat., 



XLV, p. 623. 



