SUCKLING — EMBEYONIC DEVELOPMENT IN MICE 55 



delayed implantation in the case of mice which are suckling young, 

 and also that this influence of the mammary glands is subject 

 to marked individual variation. 



4. The suckling by pregnant female mice of the same number 

 (four in this experiment) of young will not necessarily lead to 

 either synchronous development of embryos or the same length 

 of gestation periods. The only explanation that can be offered 

 at the present time for this lack of uniformity is the individual 

 variation, noted in the preceding paragraph, of the inhibition 

 from the mammary glands or in the strength of the counteracting 

 forces, probably due to metabolic idiosyncrasies. 



LITERATURE CITED 



Adler, L. 1912 Versuche mit 'Mammimum Poehl' betreffend die Function 

 der Brustdriise als innerlich sezernierende Organ. Miinchner Med. 

 Wochenschrift, 59. 



Daniel, J. F. 1910 Observations on the period of gestation in white mice. 

 Jour. Exp. Zool., vol. 9, no. 4. 



KiRKHAM, W. B. 1916 The prolonged gestation period in nursing mice. (Ab- 

 stract.) Anat. Rec, vol. 10, no. 3. 



1916 The prolonged gestation period in suckling mice. Anat. Rec, 

 vol. 11, no. 2. 



