204 



It has been suggested, with very good reasons, that brachypte- 

 rons forms are more prolific than macropterous ; this, if cor- 

 rect, wonld account, on selective lines, for the predominance 

 of brachypterons forms in our Delphacid fauna; this would 

 likewise lead to stricter segi-egation and thence to species 

 formation. 



The elongation of the head of D ictyoporodel ph ax mirahilis 

 may also represent the result of Natural Selection, for Ker- 

 shaw has sho^^'ll that among some Ilomoptera there is a great 

 expansion of the stomach, wdnich sends diverticula into every 

 available portion of the body. In D. mirahilis, Pyrops can- 

 delaria and some other species one of these diverticula enters 

 the head and fills the entire enlarged portion. It appears 

 as if some physiological necessity (perhaps on account of the 

 nature of the food) made an enlargement of the stomach ad- 

 vantageous. But if Xatural Selection has brought about a 

 monotypic evolution in this case it has not given it any ad- 

 vantage over other species, for D. ntira/jilis has an exceedingly 

 restricted range. 



When we consider coloration there are certain cases which 

 look as if ^Natural Selection could have pla^^ed some part. 

 The nymphs and adults of N esosydne hoae live on the young 

 green leaves of Acacia hoa and are similarly colored; N. rii- 

 bescens, N. pseudorubescens and N. koae-phyllodii live on the 

 dark-colored phyllodia of the same tree and are brownish or 

 reddish brown in color. N esosydne raillardiae is colored like 

 the leaves of its food-plant, and the dark body and whitish 

 tegmina of N. cyathodis are very cryptic when associated with 

 its food on the lava flows around Kilauea. It would be of 

 interest to know the habitat of N. fullawayi in Molokai, which 

 is practically only a color variety of N. cyathodis. The dark 

 colors of the Leialolia group, attached to Metrosideros, are 

 also cryptic in association wdth the main appearance of their 

 habitats. The great majority of the species of Alo]ii)ii are 

 indefinite in coloration and there is a great amount of varia- 

 tion, especially among the females, so that it is impossible to 

 insist upon any protective coloration — unless the variation 

 and indefiniteness themselves are protective. 



When we turn to the phallic characters we confront a very 

 difficult problem, for we know absolutely nothing about the 

 manner in which these organs function in the Delphacidae. 

 At one time I held an opinion similar to Prof. V. L. Kellogg, 



