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THE AMERICAN NATURALIST [Vol. L 



Crampe 7 many years ago showed from his extensive data on rats 

 that the maximum fertility was on the second litter. King and 

 Stotsenberg 8 have recently given data which lead to the following 

 averages : 



Fourth 15 6.40 



Pearson and Weldon have shown 9 that in mice there is an in- 

 crease in the mean number of young from the first to the third 

 litter, thus: 



For the rabbit Bailey, fide Hammond, 10 gives the values : 



Second 7.25 ±0.41 



Third 7.08 ±0.38 



Such data as these are of obvious importance in the physiology 

 of reproduction in the mammals. They will be of far greater 

 value when it is possible to determine the influence of the actual 

 age of the mother as well as of the order of birth upon fertility. 

 Detailed records of size as well as of number of offspring and of 

 mortality would also be of great importance. 



Relationship between Fertility and Somatic Characters 



The interrelationship between fertility and somatic characters 

 is a subject which may have a morphogenetic, genetic or eco- 

 nomic interest. 



Reference to some of the earlier literature has already been 



7 Crampe, IL, "Zucht-Versuche mit zahmen Wanderratten. I. Eesultate 

 der Zucht in Verwandschaft, " Landwirths. Jahrb., 12: 389-449, 1883. 



8 King, H. D. and J. M. Stotsenberg, "On the Normal Sex Eatio and the 

 Size of the Litters in the Albino Eat (Mns norvegicus aMnus)," Anat. 

 Becord, 9 : 403-420, 1915. 



oBiometrika, 7: 384, 1910. 



™ Hammond, J., "On Some Factors Influencing Fertility in Domestic 



