204 



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

 rons forms are more proliiie than macropterons ; this, if cor- 

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

 of brachypterous forms in our Delphacid fauna ; this would 

 likewise lead to stricter segregation and thence to species 

 formation. 



The elongation of the head of DicfyoporndeJphax minihiUs 

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

 shaw has shoAni that among some Homoptera there is a great 

 expansion of the stomach, wdiich sends diverticula into every 

 available ])ortion of the body. In D. mirahilis, Pyrops can- 

 (Jclaria 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 IS'atural Selection has brought about a 

 monotypic e\'olution in this case it has not given it any ad- 

 vantage over other species, for D. DiirahUis has an exceedingly 

 restricted range. 



When we consider coloration there are certain cases which 

 look as if Natural Selection could have played some part. 

 The nymphs and adults of Nesosydne koae live on the young 

 green leaves of Acacia I'oa and are similarly colored ; N. ru- 

 hesccms, N. pseucloruhesrcns and N. I'oae-pliyllodii live on the 

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

 reddish brown in color. Ncsosydne raillardiae is colored like 

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

 tegmina of N. cyalliodis 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. fuUawayi in Molokai, which 

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

 colors of the LeiaJoha group, attached to Metrosideros, are 

 also cryptic in association with the main appearance of their 

 habitats. The great majority of the species of AloJiini are 

 indefinite in colorati(m 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 

 difiicult ])roblem, for we know absolutely nothing al)out the 

 manner in which these organs function in the Delphacidae. 

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



