Oct. 24, 1889] 



NATURE 



625 



plants and animals, to say nothing of all the varieties 

 Avhich have perished in the struggle for existence. It 

 would, in fact, appear that Prof. Weismann denies the 

 acquisition of any new individual characters due to the 

 influence of external conditions by any except unicellular 

 organisms. 



This being his view, we find, as might be expected, 

 that Prof. Weismann opposes the assumption of the 

 transmission, by means of sexual or amphigonic repro- 

 duction, of characters which he terms "somatogenic" 

 (p. 413) ; that is, of characters which have manifested 

 themselves in the soma of an individual, not spontane- 

 ously, but as the result of the operation of external forces 

 or conditions ; and he critically sifts the evidence for 

 such transmission with results which, it must be admitted, 

 tell in favour of his views. 



For all that, Prof. Weismann does not take up an alto- 

 gether uncompromising position with reference to this 

 point ; in fact, his statements of opinion are so fluctuating 

 that it is difficult to determine what his position exactly 

 is : witness the following quotations : — 



"... and it is impossible to imagine any way in which 

 the transmission of changes, produced by the direct action of 

 •external forces upon the somatic cells, can be brought about " 

 (p. 80). 



" Hence it follows that the transmission of acquired characters 

 is an impossibility ..." (p. 266). 



" For the germ-cells are contained in the organism, and the 

 external influences which affect them are intimately connected 

 with the state of the organism in which they lie hid. If it be 

 well nourished, the germ-cells will have abundant nutriment ; 

 and, conversely, if it be weak and sickly, the germ-cells will be 

 arrested in their growth. It is even possible that the effects of 

 these influences may be more specialized ; that is to say, they 

 may act only upon certain parts of the germ-cells. But this is 

 indeed very different from believing that the changes of the 

 organism which result from external stimuli can be transmitted 

 to the germ-cells, and will re-develop in the next generation at 

 the same time as that at which they arose in the parent, and in 

 the same part of the organism " (p. 103). 



" Still we cannot exclude the possibility of such a transmission 

 occasionally occurring ; for, even if the greater part of the 

 effects must be attributed to natural selection, there might be a 

 small part in certain cases which depends on this exceptional 

 factor. 



"A complete and satisfactory refutation of such an opinion 

 cannot be brought forward at present ; we can only point out 

 that such an assumption introduces new and entirely obscure 

 forces, and that innumerable cases exist in which we can 

 certainly exclude all assistance from the transmission of acquired 

 characters" (p. 100). 



"If, on the other hand, acquired differences are transmitted, 

 this would prove that there must be something wrong in the 

 theory of the continuity of the germ-plasm, as above described, 

 and in the non-transmission of acquired characters which results 

 from this theory " (p. 268). 



"It seems to me that the problem of the transmission or 



non-transmission of acquired characters remains, whether the 



1^ theory of the continuity of the genn-plasm be accepted or 



rejected " (p. 403). 

 » 



I would remark, with reference to the statement that it 

 is impossible to imagine any way in which somatogenic 

 changes can be transmitted, that such a transmission is 

 quite conceivable, and is even probable, when the con- 

 tinuity of the somatoplasm is borne in mind. If the ovum 

 contains somatoplasm, as we are driven to assume, and 

 if, as cannot be denied, the somatoplasm takes part in 

 the formation of the body of the embryo, then it is not 

 impossible that changes induced in the body of the 

 parent, by the action of external conditions, may be 

 transmitted to the offspring through the somatoplasm of 

 the ovum. The discontinuity of the somatoplasm must 

 be proved before the impossibility of the transmission of 

 somatogenic characters can be considered to have been 

 established. 



But if Prof. Weismann is not prepared to admit that 

 there is more than a remote possibility that variation 

 may, in some degree, be due to the transmission of 

 somatogenic characters, he makes a large concession 

 in admitting that new characters may be acquired in 

 another way, and, being transmissible, lead to varia- 

 tion. The first hint of this view is to be found on pp. 

 98, 99 :— 



" These changes — such, for example, as are produced by a 

 strange climate — have always been looked at under the supposi- 

 tion that they are transmitted and intensified from generation 

 to generation, and for this reason the observations are not 

 always sufficiently precise. It is difficult to say whether the 

 changed climate may not first have changed the germ, and if 

 this is the case the accumulation of eflects through the action of 

 heredity would present no difficulty" (p. 98). 



" It must be admitted that there ar2 cases, such as the 

 climatic varieties of certain butterflies, which raise some diffi- 

 culties against this explanation. I myself, some years ago, 

 experimentally investigated one such case, and even now I 

 cannot explain the facts otherwise than by supposing the passive 

 acquisition of characters produced by the direct influence of 

 climate " (p. 99 ; see also above quotation from p. 103). 



It is again mentioned on p. 271, but it is not 

 prominently asserted until p. 410, where Prof. Weismann 

 says : — 



" I have never doubted about the transmission of changes 

 which depend upon an alteration in the germ-plasm of the re- 

 productive cells, for I have always asserted that these changes, 

 and these alone, must be transmitted. If anyone makes the 

 contrary assertion, he merely proves that he does not understand 

 what I have said upon the subject. In what other way could the 

 transformation of species be produced, if changes in the germ- 

 plasm cannot be transmitted ? And how could the germ-plasm 

 be changed except by the operation of external influences, using 

 the words in their widest sense ? . . . " 



On pp. 402-403 Prof. Weismann defines his view more 

 clearly ; — 



"It is certainly necessary to have two terms which distinguish 

 between two chief groups of characters — the primary characters 

 which first appear in the body itself, and the secondary ones 

 which owe their appearance to variations in the germ, however 

 such variations may have arisen. We have hitherto been accus- 

 tomed to call the former 'acquired characters,' but we might 

 also call them somatogenic, because they follow from the reaction 

 of the soma under external influences ; while all other characters 

 might be contrasted as blastogenic , because they include all those 

 characters in the body which have arisen from changes in the 

 germ. In this way we might perhaps prevent the possibility of 

 misunderstanding. . . . Among the blastogenic characters, we 

 include not only ail the changes produced by natural selection 

 operating upon variations in the germ, but all other characters 

 which result from this latter cause. " 



The point is again mentioned on p. 433 : — 



" It is therefore possible to imagine that the modifying effects 

 of external influences upon the germ-plasm may be gradual and 

 may increase in the course of generations, so that visible changes 

 in the body {soma) are not produced until the effects have reached 

 a certain intensity." 



It is not a little remarkable that, after insisting so 

 strongly, as in the passage previously quoted, on the 

 extreme stability of the germ-plasm. Prof. Weismann 

 should be prepared to admit that it is in so high a degree 

 susceptible to the action of external influences. He is, 

 however, inclined to complain, in the passage on p. 410, 

 that this view of the production of blastogenic changes by 

 external influences has been ignored ; but the readers of 

 the earlier essays may well be pardoned for inattention to 

 this point, as it is only casually mentioned there, and is 

 not put forward as an integral part of his theory of varia- 

 tion. No one reading the statement of his theory of 

 variation on p. 277 would infer that Prof. Weismann 

 attached any importance to the efTect of external influ- 

 ences on the germ in producing new characters. In fact, 



