REVIEW. 419 



and since in illustration of each a mass of facts is adduced, 

 it goes without saying that occasional slips have been made, 

 and that all critics will not assent to everything. Under the 

 former head we may mention that experiment has revealed 

 in the Apteryx a wonderful power of detecting earthworms, 

 and, apparently, by the use of its olfactory powers. By way 

 of criticism we may point out that Mr. Pycraft has not 

 explained with sufficient fulness all that inevitably follows 

 from the acquisition of the power of flight. For example, 

 the head had to be lightened. Hence the loss of teeth, for 

 strong teeth involve strong and heavy jaws. Hence, for 

 some species, the necessity of a strong- walled gizzard. With 

 the acquisition of great mobility came the need of a strong 

 voice to keep the flock in touch with one another or to bring 

 the sexes together. And so from silent reptiles have come 

 loud-voiced birds. After an admirable survey of the facts 

 comes a very inadequate theory of sexual selection. It is 

 true that for a species any display, poor or splendid, may do, 

 but as soon as variation in the direction of fine plumage has 

 begun, it will not do for an individual cock-bird to be dowdy. 

 Hence male finery must be definitely due to sexual selection, 

 and not merely to the absence of natural selection. Of 

 pairing and polygamy no explanation is offered. Surely 

 the constancy of mate to mate is due to the fact that in the 

 monogamous species the assistance of the male is required 

 for the rearing or defending of the young. Lastly, it may be 

 mentioned that the index is very far from complete. But, 

 summing up, we may describe the book as a vast collection 

 of facts illuminated by stimulating theory. The illustrations 

 are many and nearly all of them excellent. 



F. W. H. 



