Of the Papuan Islands 579 



crossed the space of more tlian a thousand miles, which now 

 separates them from their nearest alHes. Such facts point to 

 changes of land and sea on a large scale, and at a rate which, 

 measured by the time required for a change of species, must 

 be termed rapid. By speculating on such changes, we may 

 easily see how partial waves of immigration may have enter- 

 ed NeAV Guinea, and how all trace of their passage may have 

 been obliterated by the subsequent disappearance of the inter- 

 vening land. 



There is nothing that the study of geology teaches us that 

 is more certain or more impressive than the extreme instabil- 

 ity of the earth's surface. Everywhere beneath our feet we 

 find proofs that what is land has been sea, and that w^here 

 oceans now spread out has once been land ; and that this change 

 from sea to land, and from land to sea, has taken place, not 

 once or twice only, but again and again, during countless ages 

 of past time. Now the study of the distribution of animal 

 life upon the present surface of the earth causes us to look 

 upon this constant interchange of land and sea — this making 

 and unmaking of continents, this elevation and disappearance 

 of islands — as a potent reality, which has always and every- 

 where been in progress, and has been the main agent in deter- 

 mining the manner in which living things are now grouped 

 and scattered over the earth's surface. And when we contin- 

 ually come upon such little anomalies of distribution as that 

 just now described, we find the only rational explanation of 

 them in those repeated elevations and depressions which have 

 left their record in mysterious, but still intelligible characters 

 on the face of organic nature. 



The insects of New Guinea are less known than the birds, 

 but they seem almost equally remai-kable for fine forms and 

 brilliant colors, The magnificent green and yellow Ornithop- 

 terae are abundant, and have most pi'obably spread westward 

 from this point as far as India. Among the smaller butter- 

 flics are several peculiar genera of Nymphalidae and Lycse- 

 nidae, remarkable for their large size, singular markings, or bril- 

 liant coloration. The largest and most beautiful of the clear- 

 winged moths (Cocytia d'urvillei) is found here, as well as the 

 large and handsome green moth, Nyctalemon orontes. The 



