CERTAIN TAXONOMIC CHARACTERS OF GRYLLUS. 17 



smaller than the means of these same organs of the long-winged group. 

 Also, the long-winged group is less variable than the short-winged 

 one. These are exactly the relations holding in the Gotha collection. 

 Table 81 shows that there is a slight difference in the correlations in 

 the two groups of the genus as a whole. The long-winged group has 

 its organs more closely correlated than the short-winged one. The 

 single exception that between the body and ovipositor is not signifi- 

 cant when we consider the probable errors and also the fact that the 

 body-length is an untrustworthy character. This stronger correlation in 

 the long-winged group is somewhat apparent also in the Gotha collec- 

 tion, but is not very marked. 



Table 10 gives the third moments for the genus as a whole. The 

 polygon of frequencies for the long-winged tegmina is significantly 

 skew toward the short-winged condition. The other polygons are 

 approximately symmetrical, as was the case with the Gotha collection. 

 I regret that it was impossible to get data as to the interspecific wing- 

 length constants. They would probably show significant skewness. 



The conclusion to be drawn from this section is, it seems to me, that 

 the local populations of Gryllus are merely samples of the genus as a 

 whole; and, although presenting sufficiently diverse values to entitle 

 them, or at least portions of them, to specific distinction, they are not, 

 as far as these taxonomically important organs indicate, organically 

 different either from each other or from the genus as a whole. The only 

 sharply defined groups in the genus appear to be those based upon the 

 dimorphism of the wing-length, and even these two groups may be 

 derived from a single female, and they freely interbreed in nature. 



4. THE EFFECT OF LOCAL DIFFERENCES IN THE ENVIRONMENT. 



The distribution of Gryllus within an area seems to be determined 

 chiefly by food-supply and shelter. It is not a grass-lover like the 

 closely related Nemobius. Its food is dried organic material, such as 

 rags, dead grass, rotten wood, partly dried cow-dung, and on beaches, 

 seaweed, shellfish, etc. All of these things also afford shelter. 



Uhler (1889) noted that G. pennsylvanicus (short ovipositor) is found 

 on loamy soils, while on the sandy beaches in the same general locality 

 the crickets have longer ovipositors. The relation between the char- 

 acter of the soil and the ovipositor hence, also, species is well brought 

 out by my three collections from Cold Spring Harbor. These collections 

 were all made at the same time and from localities within several hun- 

 dred meters of each other. 



There projects from the west side of Cold Spring Harbor a sand-spit 

 660 meters long and having an average width of about 50 meters. The 

 chief vegetation on the spit is Ammophila arenaria. Along its edges 



