26 



NA TURE 



[May io, 1906 



parent insect in tlie pupal condition, but liis argu- 

 ment does not amount to mucli ; and it may well be 

 borne in mind that an example of somewhat analogous 

 character is afforded by the alternative characters ex- 

 hibited by the leaves and other structures of many 

 amphibious plants. Many of these can assume one 

 of two different forms, the production of either depend- 

 ing on the stimulus given by the environment to the 

 embryonic tissues at the growing points. Thus the 

 form of, say, a leaf of surb. a pianc is determined 

 at a very early stage in its dovelopmr-.r, and long 

 before it is sufficiently advanced for any functionally 

 direct adaptation to a terrestrial or to an aquatic 

 environment. But when once the stimulus has 

 operated, subsequent removal to opposite conditions 

 does not result in a corresponding alteration in the 

 future development of such a leaf — it belongs definitely 

 to the aquatic or to the terrestrial type, whichever 

 line of ontogeny it embarked on from the first. It 

 would seem, at any rate for the present, and in the 

 absence of sufficient experimental evidence to the 

 contrary, more natural to regard these di- or poly- 

 morphic species as "balanced" forms; the actual 

 course of their ontogeny, whilst restricted to certain 

 directions, and confined within definite limits, depend- 

 ing on the alternative character of some metabolic 

 activity. This is, however, very different from an ad- 

 mission of the " inheritance of acquired characters." 

 For if anything at all is meant by the expression, it can 

 only imply that the hereditary mechanism has itself 

 undergone a definite and corresponding change; and 

 at present a direct influence of the environment in this 

 sense is negatived by the results of the most critically 

 conducted experiments on breeding. 



Hertwig takes up a definite position as to the 

 relation of the " somatic " to the " germ " cells. 

 He regards all the cells of the body as fundamentally 

 equivalent, though differentiation may mask and 

 finally render impossible the return of a particular cell 

 to the embryonic state. The definite tissue cell has 

 become specialised rather as the result of an im- 

 pulse from without than by a segregative process of 

 analysis; and herein he is diametrically opposed to 

 Weismann and his followers, in regarding cellular 

 differentiation as a secondary rather than as a primary 

 matter. In this he will find many who are at one 

 with him, for the " erbungleich " division postulated 

 by Weismann, which would result in development 

 consisting of a sorting out or analysis of the characters 

 of the germ, conflicts with many facts of experience, 

 and it is only by numerous " Hilfshypothese " that it 

 can be sustained for the plant and vegetable kingdoms. 

 In a notice of a book like this one of Hertwig's, it is 

 natural that the points on which diversity of opinion 

 prevails should occupy a relatively prominent place. 

 But such treatment is in no way intended to detract 

 from or to minimise the great value of the work, 

 coming as it does from one who has himself done so 

 much to advance the subject of which he writes, and 

 whose lucid and suggestive treatment of his theme 

 will always command attention. It is a book that 

 should be read by all who are interested in the ques- 

 tions of modern bioiogy. J. B. F.^^rmer. 

 NO. 1906, VOL. 74] 



APPRECIATIONS OF HAECKEL. 

 (i) Ernst Haeckel: Der Mann iind sein Werk. By 

 Carl W. Neumann. Pp. 80. (Berlin : Gose and 

 Tetzlaff, n.d.) Price 1.50 marks. 



(2) Haeckel : His Life and Work. By Wilhelm 

 Bolsche, with introduction and supplementary 

 chapter by the translator, Joseph McCabe. Pp. 

 336; illustrated. (London : T. Fisher Unwin, 1906.) 

 Price 15s. net. 



(3) Last Words on Evolution : a Popular Retrospect 

 and Summary. By Ernst Haeckel. Translated 

 from the second edition by Joseph McCabe. Pp. 

 127 ; with portrait and three plates. (London : 

 A. Owen and Co., 1906.) Price 6s. 



(i)^ /[ ANY who know Prof. Haeckel only as the 

 i' J- author of zoological memoirs, evolutionist 

 essays, and monistic propaganda, will be glad of the 

 opportunity which this brightly written booklet 

 affords of becoming more closely acquainted with the 

 man himself and with the story of his life. We read 

 with interest of the eager boy-naturalist wandering 

 on the Siebengebirge, of the apprenticeship under 

 Johannes Miiller, of the year of medical practice (if 

 a man can practise on three patients!), of the 

 eventful year in Italy during which Haeckel nearly 

 became a landscape painter, of the growing fascin- 

 ation which the plankton exerted, satisfying at once 

 his artistic and scientific interests, of the influence 

 that the " Origin of Species " had on him, and of his 

 early settlement in Jena — that " feste Burg freien 

 Denkens " — which nothing could ever induce him to 

 leave. At the Stettin Versammlung in 1863 Haeckel 

 entered the lists as a champion of the evolutionist 

 " Weltanschauung," contending almost single-handed 

 against contempt and prejudice. His cause, which 

 eventually prevailed, as the truth must, had to be 

 fought for, and those who are offended by the 

 impetuous expressions of Haeckel's " Stiirmernatur " 

 are profitably reminded by this little book of the 

 courage and indefatigability of perhaps the most virile 

 protagonist of a thesis which has been one of the 

 greatest contributions made by science to human 

 progress. The author has told the story of Haeckel's 

 life and work with vividness and enthusiasm. He 

 concludes his effective sketch by indicating, somewhat 

 too tersely and vaguely, how it has been possible for 

 him to use the truth that is in Haeckel in developing 

 a monistic philosophy more satisfying to the human 

 spirit. 



(2) Prof. W. Bolsche 's study of Ernst Haeckel is, 

 like the frontispiece to the book, a picture in warm 

 colours. The author is nothing if not enthusiastic, 

 and indeed no one can think over the achievements of 

 Haeckel's life without sharing the author's admiration 

 for his hero. If it be true, as the translator says, 

 that " a hundred Haeckels, grotesque in their unlike- 

 ness to each other, circulate in our midst to-day," 

 this " plain study of his personality and the growth of 

 his ideas " should go far to replace them by giving 

 us an appreciation approximately true. We should 

 not ourselves have called Bolsche's book, as Mr. 

 McCabe does, a "plain study," for its characteristic 

 features are exuberant enthusiasm and a brilliantly 



