5 66 



POPULAR SCIENCE MONTHLY. 



GENERAL NOTICES. 



We can hardly conceive a more fascinat- 

 ing subject than the one treated of in this 

 book.* Birds, by their song, their marvelous 

 flight, their mysterious migrations, the inde- 

 pendent intelligences among them, which 

 have led in past times to many species be- 

 coming the associates of man, offer a most 

 delightful subject for study. It is interest- 

 ing to recall the fact that Cuvier and his 

 contemporaries regarded the birds as a closed 

 type, a group that seemed completely isolated 

 from the other classes of vertebrates, and 

 now they are known to be closely related to 

 the reptiles. Mr. Headley has devoted con- 

 siderable space in his book to these reptilian 

 affinities. In bis chapter on the embryo bird 

 he might have added other reptilian charac- 

 ters, such as the claws which are seen on the 

 fingers on the embryo sea-pigeon ; particu- 

 larly he might have described more fully the 

 tarsal bones, showing that the ascending 

 process of the astragalus had an independ- 

 ent center of ossification, and represented 

 in the embryo the intermedium wedged hi 

 between the distal end of the tibia and 

 fibula as shown in the salamanders. Birds 

 may be cited for almost every point defined 

 by Darwin in his theory of natural selection, 

 not only in their reptilian affinities, as shown 

 in their embryological and paleontological 

 history, but in the very remarkable exam- 

 ples of variation in habits, color markings, 

 albinism, molting, sexual selection, protective 

 coloration, etc. The author's ideas of ho- 

 mology and analogy are somewhat obscure. 

 Having correctly defined analogy by the 

 common example of a bird's wing and an 

 insect's wing as being alike in function, but 

 different in origin of structure, and hence 

 analogous and not homologous, he proceeds 

 to say that there is no homology between 

 the wing of a bird and the wing of a bat ; 

 whereas there is the strictest homology in 

 origin, structure, and function. In the next 

 sentence he says that the tails of all verte- 

 brates are homologous, which is correct. Yet 

 here we have a few vertebrae in one tail and 

 over fifty hi another. We have the broad fin 



The Structure and Life of Birds. By F. W. 

 Headley, M. A. Pp. 417, with Illustrations. New 

 York : Macmillan & Co. Price, $2. 



of a fish, the trowel of the beaver, and the 

 climbing appendage of the monkey, and all 

 are indeed homologous. In the same way 

 limbs of the vertebrates are homologous; 

 whether it be the pectoral fin of a fish, the 

 leg of a turtle, the wing of a pterodactyl, 

 of a bird or a bat, or the arm of man, a 

 strict homology runs through them all. Mr. 

 Headley has managed his material admi- 

 rably, and one gets in a condensed form 

 many facts about birds which have been 

 brought to light within recent years. The 

 clearness of the illustrations gives an added 

 value to the book. 



A difficult problem can be solved only by 

 attacking it from one side after another. 

 Prof. Donaldson has made his contribution 

 to ascertaining the nature and action of the 

 mind by setting forth the mode of growth 

 of the chief portion of the nervous system.* 

 He introduces his specific subject by three 

 chapters discussing the general phenomena 

 of growth and the rate of increase of the 

 whole body. Then taking up the brain and 

 spinal cord, he presents statistics showing at 

 what rates these organs increase in weight 

 and what weights they attain. He finds 

 that the facts now available " contribute 

 mainly to a healthy skepticism concerning 

 the current interpretations of brain-weight." 

 The author next traces the growth of the 

 nerve elements and describes the architec- 

 ture of the nervous system, calling attention 

 to the changes of structure that are due to 

 the growth of the organism. The process of 

 dissolution in old age is also traced. Chap- 

 ters on localization of function, physiological 

 rhythms, and fatigue furnish additional data 

 for the author's discussion of the subject 

 of education, which concludes the volume. 

 From these data he finds that " education 

 must fail to produce any fundamental changes 

 in the nervous organization, but to some ex- 

 tent it can strengthen formed structures by 

 exercise, and in part waken into activity the 

 unorganized remnant of the dormant cells. 

 . . . On neurological grounds, therefore, 



* The Growth of the Brain. By Henry Her- 

 bert Donaldson. The Contemporary Science 

 Series. Pp. 374, 12mo. London : Walter Scott, 

 Ltd. Price, 3*. Gd. New York : Charles Scrib- 

 ner's Sons. Price, $1.25. 



