THE VARIATION AND CORRELATIONS OF CERTAIN TAXONOMIC 



CHARACTERS OF GRYLLUS. 



INTRODUCTION. 



As a result of the formulation of the doctrine of evolution, the last 

 half-century has been characterized by a zealous study of organic vari- 

 ation from a number of viewpoints. A recent phase of this work, and 

 the natural outcome of the desire to gain exact information upon dis- 

 puted or doubtful points is the statistical science known as biometry. 

 The following paper is an attempt to apply biometrical methods to the 

 study of the variation and correlations of certain of the taxonomically 

 important characters of a number of closely related species. 



Much, of course, depends upon the choice of the material to be used 

 in such a study. In the first place, it ought to be something which is 

 abundant and easily obtained. A satisfactory study of variation can 

 not be made from a few specimens; and when the whole field lies be- 

 fore one it would be foolish to choose a form which would be difficult 

 to procure. It is also desirable that the group selected should be wide- 

 ranging, both geographically and physiographically. Otherwise it can 

 throw but little light upon geographic variation and the influence of 

 the environment. Furthermore, for a study of variation we should 

 select something which is variable. The characters must be measur- 

 able and should be things which are not affected by growth or from 

 which the growth factor is easily eliminated. 



This latter consideration points to the Arthropods as a valuable source 

 of biometric material. Insects, at least, do not grow after they have 

 reached the easily recognizable adult state. They are, moreover, very 

 abundant and easily collected, and the dimensions of the taxonomic 

 characters of most of them do not change in preservation. Now, of 

 insects there are few more abundant, of a wider distribution, more 

 variable, or possessing characters more easily measured than the com- 

 mon crickets (Gryllinse). Having this in mind, the following work 

 was carried out upon the typical genus, Gryllus. 



The work was started under the direction of Dr. C. B. Davenport, 

 who has also kindly read the manuscript. To him, both as teacher at 

 the University of Chicago, where most of the calculations were made, 

 and as Director of the Station for Experimental Evolution of the Car- 

 negie Institution of Washington, where they were completed, I am 



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