READERS of the late Mr. Shelf ord's Naturalist in 

 North Borneo, edited by Edward B. Poulton (Fisher 

 Unwin), will experience a deep feeling of regret that the 

 urbane, attractive, sane personality of the writer, impressed 

 on every chapter of the book, should be lost to science and 

 to literature. Professor Poulton, in editing a work left 

 incomplete at the time of the author's early death, has 

 admirably accomplished his task. The book is full of 

 important facts for the professional biologist, facts 

 gathered by first-hand study of living nature as well as 

 by laboratory work. Lovers and students of Natural 

 History will be enthralled by the descriptions and dis- 

 cussions provided for him in a manner at once pleasant 

 and lucid. The extraordinary facts narrated in the 

 chapter on " Ants and Plants " remind us of an entertain- 

 ing essay by the late Father Gerard, S.J., in which he 

 called attention to some of the difficulties these curious 

 facts raised in connection with the evolutionary hypo- 

 thesisdifficulties not yet cleared up. Quite a number of 

 plants of various Natural Orders exhibit " curious modifi- 

 cations of structure, such as huge bulbiform swellings 

 galleried in all directions, tubular stems and roots, and 

 curious appendages, which structures are constantly in- 

 habited by ants." Now the interesting query arises : 

 Are the structures developed for the benefit of the ants, 

 and if so what has caused this apparently altruistic action ? 

 Or have the ants made use of passages constructed by the 

 plant for its own purposes, and if so what were the pur- 

 poses for which the structures were formed ? When one 

 reads the title of " Mimicry " at the head of a chapter, 

 written by Mr. Shelford and edited by the distinguished 

 Hope Professor of Entomology at the University of Ox- 

 ford, one necessarily forms high anticipations of what it 



is likely to contain. Nor were we disappointed. The 

 chapter in question is profoundly interesting. Particular 

 attention is due to the important statement now to be 

 quoted as it deals, and very judiciously, with matters at 

 this moment of paramount interest to the biological 

 world : " Whole-hearted supporters of natural selection 

 regard variation as indefinite and infinite, and only con^ 

 trolled by natural selection ; but I am heretic enough to 

 believe that variation is defined and limited and con- 

 trolled only partially by natural selection. I regard the 

 lines along which variation in any organisni can proceed 

 as limited in number ; to use a metaphor j I look on 

 variation as an engine which can proceed only along certain 

 fails. There may be numbers of such rails going in dif- 

 ferent directions, but the engine cannot get off the rails." 



