28 



Scientific Proceedings (55). 



mammae, unless there is some peculiarity of feeding habits in 

 the young which would nullify the advantage, not to say necessity, 

 of having enough nipples to "go around." It would seem, a 

 priori, that natural selection should have operated to bring about 

 a high correlation, both intra- and interracial between these two 

 variables, size of litter and number of mammae of the dam. The 

 purpose of this paper is to present the results of a study of inter- 

 racial correlation between number of mammae and size of litter. 



Data. 



The most extensive series of statistics regarding size of litter 

 and number of mammae which I have been able to find is that given 

 by Bellingeri 1 in a treatise on " Mastologia." 



Bellingeri gives (loc. cit., p. 84) a table including something 

 over a hundred different species of wild and domestic mammals, 

 representing all the orders of Mammalia, in which so far as possible 

 the following information is given for each species: number of 

 mammae in the female, number of young born at a birth, breeding 

 season, and certain data respecting breeding and feeding habits. 

 So far as it has been possible to check the records against more 

 modern work they have been found to be in general correct. In 

 using the material all doubtful and incorrect cases which could 

 not be corrected from available literature have been eliminated. 

 Further there are a certain number of species for which informa- 

 tion on one or more of the points tabled is lacking. After all 

 these eliminations there are left 90 species for which there are 

 complete (so far as concerns the present problem) and presumably 

 accurate records. 



In dealing with the material biometrically it has been necessary 

 to make certain assumptions. In a number of instances the figures 

 given for both number of young and number of mammae are the 

 limits of the range of intraracial variation rather than the intra- 

 racial mode, mean or median. In such cases it is necessary to 

 make an approximation to the intraracial mean before the figures 

 can be entered in a correlation table. In reaching these approxima- 



1 Bellingeri, C. F., "Delia fecondita e della proporzione dei sessi nelle nascite 

 degli animali vertebrati, e mastologia, con considerazione anatomico-fisiologichi sul 

 numero e posizione delle mamelle," Tome III, Torino, 1849. 



