CERTAIN TAXONONIC CHARACTERS OF GRYLLUS. 



13 



the most common one. In other words, the variation curve, instead of 

 being symmetrical is one-sided. The tendency of biologic frequencies 

 seems to be to group themselves symmetrically about the most common 

 condition. Whenever there is a deviation from this "normal" distribu- 

 tion it is worthy of note. In the only two cases of dimorphism, similar 

 to the present one, which have been studied (Davenport, 1901) a marked 

 skewness has been found and the two curves were skew toward each 

 other. The value of the third moment (/*,,) of the curve about its mean 

 forms a test of symmetry. In symmetrical curves it is zero within its 



probable error of 0.6745o- 3 */ where the standard deviation and 



N - the number of individuals. The sign of fs indicates the direction 

 of the skewness. Table 7 gives these values for this material and 

 shows a condition which is rather surprising. None of the curves show 

 a marked asymmetry, all the third moments being less than three times 

 their probable errors. 



TABLE 7. Third moments of the Gotha, Florida, collection. 



To sum up this section, the Gotha collection is strikingly dimorphic 

 with respect to wing-length. Dimorphism is noticed, to a lesser degree, 

 in the other organs. The short-winged group is slightly more variable 

 than the long-winged one. The correlations and regressions are prac- 

 tically the same in both cases. The variation curves are symmetrical. 



3. COMPARISON OF INTRASPECIFIC AND INTERSPECIFIC CONSTANTS. 



The opportunity here presented to study the relation between intra- 

 specific and interspecific constants for a number of organs of a lower 

 animal is, I believe, novel. The data are given in the Appendix. The 

 viewpoint in this section is that the genus Gryllus is a unit. In obtain- 

 ing the material for the preceding sections individuals selected at ran- 

 dom from one locality at one time were used. I wish now to consider 

 the species in the light of an individual, and to study specimens col- 

 lected from here and there, all over the world, having only this in com- 

 mon, that they are all of one sex (female) and that they all belong to 

 the genus Gryllus. To do this I went to the British Museum and by 

 the courtesy of the authorities measured their entire collection of Gryl- 

 lus females. There were about 175 of these and only occasionally was 



