18 



THE VARIATION AND CORRELATIONS OF 



there is always a mass of flotsam and jetsam, and under these Gryllns 

 is very abundant. Nemobius does not occur, except near the base of 

 the spit where the sand-grass is fairly thick. The majority of the 

 specimens in the "apex of spit" collection came from the very tip of 

 this spit. The majority of those in the "base of spit" collection were 

 caught within 50 meters of the actual base. Very few in either collec- 

 tion came from near the boundary between the two areas, which, for 

 convenience, I put at a county-line landmark near the middle of the 

 spit. The "mainland" collection is from an area of about 5 ares at the 

 head of the harbor, just above the storm high-water mark, along the 

 edge of the salt-marsh. The soil of the latter locality contains consider- 

 able humus, supporting a fair growth of Poa. The soil at the apex of 



the spit is practically clear 

 sand. That of the base is 

 sand, with a small amount 

 of humus. 



Over 200 females from 

 each of these three places 

 were measured. Refer- 

 ring to the results (table 

 34) , we see that the aver- 

 age lengths of the ovipos- 

 itor differ to a great ex- 

 tent and that the differen- 

 ces are progressive, i. e,. 

 the length of the oviposi- 

 tor increases as we pass 

 from the mainland to the 

 tip of the spit, being on 

 the average about 18 mm. 

 on the mainland, 19 at the 

 base of the spit, and 20 at 

 the apex. The tegminal 

 and wing differences, while not so large, are also progressive, and, con- 

 sidering the probable errors, are doubtless significant. It is interesting 

 that these organs both grow shorter instead of longer as we pass from 

 the mainland to the apex of the spit. The lengths of the posterior 

 femora are the same in each of the collections. In other words, there 

 is not only a progressive change in size, most marked in the case of the 

 ovipositor, but a striking change in proportions. In fig. 6 I have plotted 

 the polygons of frequency for the ratio of ovipositor totegmina in order 

 to show this graphically. 



The differences in variability (see table 34) are not so striking. In 

 general, the coefficients of variation are greatest in the collection from 



FIG. 6. Polygons of frequency for uitio Of ovipositor to teg- 

 minafor mainland ( ), base of spit ( ), 



and apex of spit (....) at Cold Spring Harbor, New York. 



