CONTENTS. 



Part I. — Historical. 



page. 



Theory of multiple factors 9 



Examples of multiple factors 11 



Color differences 11 



Form differences 13 



Size differences 14 



Structural characters 15 



Physiological characters 16 



Crosses between similar lines 17 



Transgressing segregation 18 



Size characters showing Mendelism 20 



Size characters seeming to "blend " 21 



Part II. — Experimental. 



Introduction 25 



Role of environment 25 



Material 29 



Crosses 29 



Studies of skeletal measurements 31 



Measurements recorded 31 



Statistical treatment 33 



Coefficients of variability, litter by litter 33 



Coefficients of size 34 



Classification in relation to parents 37 



Summary 39 



Studies of adult weight 43 



Growth curves 43 



Coefficients of variability 43 



Summary 44 



Conclusions 44 



Experimental 44 



Theoretical 45 



Bibliography 47 



Appendix: The nature of size factors as indicated by a study of correlation 51 



