RELATION OF RACE CROSSING TO THE SEX RATIO. 1 95 



mit Bruder, Enkel, Urenkel, Vater und Grossvater) ein sehr 

 verschiedenes, ja in einigen Fallen kamen sogar in der dritten 

 Geschlechtsfolge, ganz in Gegensatze zu der altercn AimaJnne^ 

 iibervviegend weibliche Nachkommen zur Welt." 



Investigations systematically directed towards determining in 

 what way and to what extent either hybridizing or inbreeding 

 affect the sex ratio are very few in number. Davenport {loc. cit), 

 from a tabulation of the sex of 377 fowls reaches the conclusion 

 already stated regarding the influence of hybridization. Schultze^ 

 has studied in mice the effect of inbreeding of various degrees 

 including the closest " Inzestzucht " on sex determination, and 

 reaches the conclusion that in general it has no effect. 



The search for factors which may determine or influence sex is 

 being actively prosecuted by experimental biologists. Any data 

 tending to throw light on the significance of any supposed sex- 

 influencing factors can but be welcome. The quotations from the 

 literature which have been given suffice to indicate that the char- 

 acter of a mating must at least be accorded the place of a " sup- 

 posed " sex-influencing factor. It is the purpose of the present 

 paper to exhibit and discuss certain data which have a direct and 

 definite bearing on the question of the significance of this factor 

 in the case of one organism, namely, man. 



The data which form the basis of this paper are extracted from 

 the published vital statistics of the city of Buenos Ayres. For 

 nearly twenty years past this city has maintained an elaborate 

 system of municipal statistics. Indeed its system might in many 

 respects well serve as a model. It is doubtful whether the sta- 

 tistics of any other city or country surpass those of Buenos Ayres 

 in completeness and accuracy. These records are published in 

 annual volumes, of which fifteen have appeared. The statistics of 

 births given in these volumes are particularly detailed. Among 

 other matters of general biological interest there is given each 

 year a table setting forth the number of births occurring in the 

 year covered by the volume, classified in such way that it appears 

 for each child born whether it was {a) male or female, {b) legiti- 



1 My italics. — R. P. 



^Schultze, O. " Zur Frage der geschlechtsbildenden Ursachen." Arch, inikr. 

 Anat., Bd. 63, Heft, i, 1903. 



