126 EVOLUTION AND ANIMAL LIFE 



Mr. S. B. Wilson remarks: "Nature has shown great sym- 

 metry in regard to the species of this genus {Hemignathus 

 inchiding Heterorhynchus) to be found in the Sandwich Archi- 

 pelago, three of the main islands having each a long-billed 

 and a short-billed form." This, of course, is most natural. 

 Both long-billed forms {Hemignathus) and short-l^illed forms 

 {Heterorhynchus) have spread from the island where they were 

 originally developed to the other islands, each changing as it 

 is isolated from the main body of the species and subjected 

 to natural selection under new conditions. With the genus 

 Heterorhynchus, the forms with slender bills reach their culmina- 

 tion. 



Going back to the original stock, to which Oreomystis 

 hairdi is perhaps the nearest living ally, we note first a divergeifce 

 in another direction. In Rhodacanthis, the bill is stout like 

 that of the large finch, not longer than the rest of the head, 

 and curved downward a little at the tip. The species of this 

 genus feed largely on the bean of the acacia and other similar 

 trees, varying this with caterpillars and other insects. The 

 stout bill serves to crush the seeds. In Chloridops, the bill is 

 still heavier, very much like that of the grosbeak. Chloridops 

 kona is, according to Mr. Robert Perkins, a dull, sluggish, 

 solitary bird and very silent; its whole existence ma}^ be summed 

 up in the words "to eat." Its food consists of the fruit of the 

 aaka (bastard sandal tree), and as this is very minute, its whole 

 time seems to be taken up in cracking the extremely hard 

 shells of the fruit, for which its extraordinarily powerful bill 

 and heavy head are well adapted. 



"The incessant cracking of the fruits, when one of these birds is 

 feeding, the noise of which can be heard for a considerable distance, 

 renders the bird much easier to get than it otherwise would be. Its 

 beak is always very dirty with a brown substance adhering to it which 

 must be derived from the sandal nuts." 



In Psittacirostra and Pseudonestor the bill suggests that of 

 a parrot rather than that of a grosbeak. The mandibles are 

 still very heavy, but the lower one, as in Heterorhynchus, is 

 short and straight, while the much longer upper one is hooked 

 over it. Pseudonestor feeds on the larvae of wood-boring beetles 

 {Cly tonus) found in the koa trees, {Acacia jalcata), while tlic 



