24 THE VARIATION AND CORRELATIONS OF 



is also true that in a dimorphic population the long-winged group has a 

 greater mean tegminal length than the short-winged one. A glance at 

 table 11 shows that, while there is a tendency for the tegmina to 

 increase as we go southward, it is not so marked as in the case of the 

 wing-length. Probably geographic influences have little direct effect. 

 The size of the tegmina may be the resultant of local environmental 

 influences upon them and their organic correlation with the wings, 

 which are modified by climatic influences. 



It is difficult to take a satisfactory world-wide survey of this subject, 

 because of the lack of data and the practical impossibility of supplying 

 this deficiency. However, the data I have for the genus as a whole do 

 not show any constant relation between geographic distribution and 

 either size or proportions of the organs studied. This fact, taken in 

 connection with the results of the study of the collections from the 

 United States, indicates that the susceptibility of Gryllus to local envi- 

 ronmental conditions overcomes or masks any tendency to geographic 

 variation which may exist, except as regards wing-length. 



6. THE BEARING OF THE DATA UPON THEORIES OF EVOLUTION. 



It should be borne in mind, when considering the bearing of the facts 

 here presented upon current theories of evolution, that Gryllus is not 

 an exceptional case. As I have mentioned before, specific distinctions 

 in this genus are just as sharp and based upon the same sort of char- 

 acters as the species in other genera, not only of the Gryllidae, but of 

 other famlies of the Orthoptera and also of other orders of animals. 

 Gryllus and Nemobius are very common, insects, and the intergrades, so 

 troublesome to taxonomists holding the specific entity idea, are met 

 with rather frequently. But the intergrades are just as certainly pres- 

 ent in other genera; only, since so many specimens of these other 

 genera are not found, intergrading specimens are rarely met with. 

 Atlanticus is a genus of the Locustidas which is not common in eastern 

 United States. Two species, dorsalis Burm. and pachymerus Burm., 

 are described. It has been my fortune to find but one specimen of this 

 genus. It was from Cold Spring Harbor, New York. The ovipositor 

 of this individual is 22 mm. long. Beutenmuller (1904) gives 30 mm. 

 as the length of the ovipositor of dorsalis and 20 mm. of pachymerus. 

 It is thus, for this character, nearer pachymerus. Its posterior femora 

 are 25 mm. long. The femora of dorsalis is 27 mm., and of pachymerus 

 22 mm. It is, then, for this character, nearer dorsalis. And so with 

 the other less important characters it is decidedly intermediate. I have 

 no doubt that Atlanticus is a case like Gryllus. Owing to the small 

 number of individuals in the former genus, however, a biometric proof 

 of this would be difficult. 



