524 SCIENCE PROGRESS 



were two fundamental types, one which he called " palseognathine," characteristic 

 of the struthious birds, the other that he called " neognathine," characteristic of 

 higher birds ; moreover he showed that the neognathine bird passed through 

 a palcEognathine stage. Thereupon Mr. Pycraft plunged into a familiar pit, 

 in which, it is true, he is in the company of perhaps a majority of systematic 

 zoologists. His major dichotomy of living birds is into Palceognathi and 

 Neogna/h!\ whereas his own discovery that all birds have once been palaeognathine 

 makes the presence of that character useless as an indication of affinity. 



In three interesting chapters (iv, v, vi) Mr. Pycraft supplies an able sketch of 

 geographical distribution, habitats and migrations of birds, showing very clearly the 

 interdependence of these phenomena. He wisely refrains from any categorical 

 theory of migration, but plainly leans to the view that it arose from seasonal 

 variations in food supply, and that the continued incidence of such economic 

 pressure has gradually increased the range of movement. He believes that the 

 routes of migration are a family tradition, slowly altered by geographical changes 

 but so definite that when, for instance, English migrants become extinct, their 

 places will not be taken by other birds of the same species, as the latter have a 

 different traditional summer or winter home. Chapters vii to ix sketch the 

 relations of birds to animate nature, to plants, to various kinds of mammals and to 

 one another. The instances selected are chosen from a wide range, including 

 such varied subjects as the agency of birds in the dispersal of plants, the parasitic 

 habits of the cuckoos and various cases of social instincts. In chapter x Mr. 

 Pycraft gives a careful and very interesting summary of the peculiar features 

 of the relations of the sexes in birds ; in another chapter (xxi), perhaps designedly 

 far removed from his description of the facts, he gives a brief discussion of sexual 

 selection. He deals with the problem in a fashion that is suggestive rather than 

 conclusive, and is plainly not satisfied that the theory of sexual selection is a 

 sufficient explanation of sexual coloration and display, antics and song. Nothing 

 could be better than his series of chapters (xi to xvi) on nests and eggs, the care 

 of offspring, the plumage of chicks, and so forth. It is a part of the subject 

 to which he has given great attention, and his presentment of the facts and 

 selection of suitable illustrations are alike admirable. It is a pity however that 

 Mr. Pycraft did not refer to the passage in Notes by a Naturalist on H.M. 

 " Challenger'''' before regretting, in a superior way, that Moseley did not examine 

 the alleged pouch of King Penguins and compare it with the marsupial pouch. 

 He would then have found that Moseley did not use the word " pouch " in a 

 structural sense, but described the fold of skin and the mode in which the &%g 

 is supported by the feet of the penguin. 



Mr. Pycraft's interpretations of the very varied conditions of nestlings is novel 

 and convincing, and is a marked advance on the conclusions of other writers. He 

 believes that the Hoatzin represents a surviving primitive condition. There is 

 enough food-yolk to allow development to proceed to such a stage that the newly 

 hatched bird can creep about actively in the branches of the tree which contained 

 the nest. By a series of adaptations, birds which lay their eggs on the ground or 

 in exposed places have come to produce still more precocious nestlings fully 

 fledged and capable of great activity as soon as they are hatched ; in other cases, 

 chiefly where nestlings if too active would fall out of the nest and be killed, 

 the food-yolk has been reduced and the young are hatched in a helpless state. 

 In yet other cases, birds which must be supposed to have had precocious nestlings 

 comparatively recently have changed their habitat, and the rate of development 

 of the young has been retarded secondarily. 



