69(5 



THE AMEBIC AN NATUBALIST 



[Vol. L 



purity. And back of this is an obscure history for the material 

 with no evidence it seems to me that Lamarckiana was ever 

 present as a native species of any flora. The chief value which 

 the study of my Lamarckiana-like hybrid may have for the prob- 

 lem of the origin and status of CEnothera Lamarckiana is likely 

 to be a clearer understanding of how an obviously impure 

 species, neo-Lamarckiana, may arise, a species which seems likely 

 to present a breeding behavior parallel to that of Lamarckiana, 

 and most important of all the significance of sterility in the 

 working out of these results. It appears to me a matter of no 

 vital importance to the status of a hybrid whether its parents are 

 pure or impure. If markedly impure the problem of analysis 

 for future generations merely becomes the greater. Since no 

 species of CEnothera has as yet passed the tests for a pure species, 

 we are at present in all of the CEnothera work talking of an ab- 

 straction when this concept is considered. 



Bradley Moore Davis 



University of Pennsylvania, 

 August, 1916 



STATISTICAL STUDIES OF THE NUMBER OF NIPPLES 

 IN THE MAMMALS 



It is perhaps not unnatural that a subject of such fundamental 

 interest as that of the nourishment of the young in the mammals 

 should have attracted the attention of observers from the time of 

 the Greek philosophers. It is only within the last few years that 

 attempts have been made to solve various problems by the appli- 

 cation of the statistical method to series of quantitatively re- 

 corded data. 



The materials may be divided for convenience of review. 



Type, Variation and Correlation in Number op Mammje 



The statement made by Parker and Bullard, 1 on the basis of 

 their splendid series of data for swine, that the standard devia- 

 tion of the number of nipples is 0.6906 in the males and 0.7905 

 m the females at once arouses the suspicion of a biometrician. 

 The constants actually are : 



i Parker, G. H, and C. Bullard, "On the Size of Litters and the Number 

 o lpples m Swine," Proc. Amer. Acad. Arts and Sci., 49: 399-426, 1913. 



