CERTAIN TAXONOMIC CHARACTERS OF GRYLLUS. 21 



amount and quality of the food is probably one of the important fac- 

 tors. At Cold Spring Harbor the posterior femora show no significant 

 differences in the three areas, but the tegmina and wings do, decreas- 

 ing as the ovipositor increases. 



The apex of the sand-spit is connected with the mainland only via the 

 base of the spit; and, as these short- winged crickets neither swim nor 

 fly, the Gryllu* population of this area must have come from the base 

 of the spit. We must consider that the characteristics of the apex pop- 

 ulation have been derived from those of the base population either by 

 selection with respect to the size of one or more organs (and the con- 

 sequent modification of all organs correlated with these), or by non- 

 selective modifying influences, or by a combination of the two. We 

 have some evidence to support the view that the ovipositor has been 

 selected for greater length, thereby decreasing the variability and cor- 

 relations. If we select from the base population a group having the 

 same mean and variability of the ovipositor as that of the apex popula- 

 tion, would we get a group closely resembling the one actually found 

 at the apex? This could be done by means of Pearson's (1902) methods. 

 However, it is not necessary to go into this rather involved bit of math- 

 ematics, as inspection will give a very definite answer. There are 

 strong positive coefficients of correlation between the ovipositor and 

 the other organs. Therefore, the group selected from the base popula- 

 tion with a view to increasing the length of the ovipositor would have 

 greater mean lengths of tegmina, wings, and posterior femora than the 

 parent population. But just the opposite is true of the natural apex 

 group. The selected group differs more widely from the apex popula- 

 tion than the base population taken as a whole. On actual calculation 

 it was found that the case of the tegmina is the worst, the difference 

 of the means being 18 times the probable error of the mean of the 

 apex, so that it seems certain that the differentiation of the organs other 

 than the ovipositor has not been brought about solely, at least, through 

 the differentiation of the ovipositor and the consequent modification of 

 the others due to correlation. What the factors factors which act 

 strongly enough to more than overcome the positive correlation between 

 the ovipositor and tegmina, for instance are, I can not say. The points 

 I wish to make now are that there are real differences between the popu- 

 lations in these three closely situated habitats, and that the differences 

 in the ovipositor are probably connected with soil differences. 



