CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY OF THE 

 MUSEUM OF COMPARATIVE ZOOLOGY AT HARVARD COLLEGE, 

 E. L. MARK, DIRECTOR, No. XCIL 



A CONTRIBUTION TO THE STUDY OF INDIVIDUAL 

 VARIATION IN THE WINGS OF LEPIDOPTERA. 



By William L. W. Field. 



Presented by E. L. Mark, April 13, 1898. 



I. Statement op the Problems. 



This paper gives the results of an attempt to fiud, in a particular 

 species, answers to the following questions : — 



1. Is a part, developed in any given species in an extraordinary 

 manner as compared with the development of the corresponding part in 

 other allied species, more variable than parts which exhibit less specific 

 peculiarity ? 



2. Which sex is the more variable ? 



The first question is raised to test, by quantitative methods, the law of 

 variation enunciated by Darwin (Origin of Species, 6th edition, §§ 220, 

 221). It is unnecessary to argue the importance of tests of this kind. 

 From data offered by others we may obtain quantitative expressions of 

 certain cases. Thus, while in nearly all groups of Mammals except the 

 sloths the number of cervical vertebrae is 7, it is a familiar fact that in 

 this aberrant group the number varies from 6 to 10. Bateson ('94) 

 gives the following data obtained from fifty-seven individuals belonging 

 to the genus Bradypus : — 



No. of Cervical Vertebra; 8 9 10 



No. of Cases 6 46 5 



Mean, 8.98+- Average Deviation from Mean, 0.21—. 



With regard to the characteristic under consideration, the Average 

 Deviation for other Mammals will be 0.00-|-. The comparison of these 

 two Average Deviations gives us a measure of the greater variability of 



