36o 



NATURE 



[September 8, 1923 



resident in the embryonic tissues ; the effects of usage 

 in the parent can have no influence on the machinery." 



Sir Arthur, therefore, if I understand him aright, 

 comes out as a predestinarian orthogeneticist. The 

 experiences of the animal have no influence in shaping 

 the structure of its offspring. In this attitude he 

 outdoes that ultra-mendelian Prof. Morgan, of New 

 York, who, when confronted with the problem of the 

 ultimate causes of liis " mutations," admitted that 

 no other source could be found for them except the 

 influence of the environment. 



What reasons does Sir Arthur adduce for what I 

 may term his despairing conclusion ? In the last 

 analysis they reduce themselves to two, namely : (i) 

 functional adaptations — such as the shape of the 

 crowns of the molar teeth — and the separation of the 

 peronaeus tertius muscle from the extensor muscle 

 of the little toe, come into existence in the embryo 

 before there is any possibility of the performances 

 of the functions to which they are adapted ; and (2) 

 Sir Arthur can conceive of no mechanism by which 

 the habits of the parent can influence the embryonic 

 machinery. 



Now when Lamarckism is dismissed on grounds 

 such as these, it would have been just as well if Sir 

 Arthur had made himself acquainted with the form 

 in which the Lamarckian theory is held by modern 

 biologists. May I briefly refresh his memory ? 

 Modern Lamarckism may be stated as follows : 



(i) An animal exposed to a new environment 

 modifies its habits, so as to adapt them to new needs. 



(2) New habits, persistently indulged in, entail 

 modifications of adult structure. 



(3) The offspring of animals which have adopted 

 the new habit, if they remain in the same environment 

 as their parents, tend to assume the new habits more 

 quickly and on slighter stimulus than did their 

 parents, and to develop the corresponding structures 

 at an earlier period of their lives. 



(4) Ultimately, when the new habits have persisted 

 for a long time, the corresponding structures make their 

 appearance in development before the performance of the 

 functions to which they are adapted. 



It is obvious, therefore, that all Sir Arthur Keith's 

 arguments against " use-inheritance " are irrelevant 

 to the question at issue. Sir Arthur is a brilliant 

 mammalian embryologist. Were he a comparative 

 embryologist he would be acquainted with cases 

 which would stagger even him in his opposition to 

 Lamarckism. I will give one. All Macruran Crustacea 

 (lobsters, prawns, shrimps, etc.), when seeking retreat, 

 move backwards and strive to thrust the abdomen 

 into a dark crevice. The hermit crabs have adopted 

 the habit of inserting the abdomen into the curved 

 passage of an empty gastropod shell, and in consequence 

 the abdomen has become curved. The young hermit 

 crab, however, in its last free-swimming stage has 

 an abdomen as symmetrical as that of a shrimp ; 

 but when it sinks to the bottom, before it has 

 found an appropriate shell, the abdomen has already 

 become curved. Does Sir Arthur ask us seriously to 

 believe that this curvature has been produced by 

 some mystical " adaptational " mechanism among 

 " embryonic cells," and has had no relation to 

 parental habits ? The paragraph in " Current Topics 

 and Events ' ' rightly states that the crux of the whole 

 discussion is the proof of the actual existence of 

 use-inheritance. Many of us believe that by means 

 of well-thought-out and patiently executed experi- 

 ments this proof has already been given. Those who 

 refuse their assent may be divided into two classes, 

 namely : (a) those who are unacquainted with the full 

 details of the experiments ; (fe) those who are 

 acquainted with these details and strive to escape from 



NO. 2810, VOL. 112] 



■phlU 



ts goes 

 .ite use- 

 ax, which 

 1 workers 

 which I 

 until the 



their inevitable conseauences by attributing fraud 

 to the experimenter. It is obvious from his sympa- 

 thetic references to Kammerer that Sir Arthur Keith 

 belongs to the first of these categories. May I reajm- 

 mend to him a more prolonged and extensive stud\ of 

 Kammerer's papers ? 



The paragraph in " Current Topics 

 on to state that every failure to 

 inheritance strengthens the Darwiniai 

 is adopted by the best and most philo 

 in biology to-day. This is a statement 

 frankly fail to understand. Darwin was 

 close of his life a convinced believer in the existence 

 of use-inheritance, although he did not regard it as 

 the sole factor in evolution. Who are at present the 

 best and most philosophical workers in biology is, 

 of course, a matter of opinion : I should think that 

 Darwin, if still with us, would put in this category 

 those who had the widest acquaintance with facts. 

 If this criterion be granted, then I may remark that 

 the best palaeontologists and the b^t systematic 

 zoologists whom I know are strongly inclined to 

 adopt the Lamarckian point of view. 



Far be it from me to say a single word in disparage- 

 ment of that great biologist Huxley, whom Sir Arthur 

 Keith claims, and I have no doubt rightly, as a 

 predeterminist. From Huxley I received my first 

 attraction to the study of biology, and it has fallen to 

 my lot to succeed him in his chair. I am convinced 

 that if Huxley were still alive, and had learned from 

 Sir Arthur Keith's brilliant exposition the wonderful 

 facts of the indifference of embryonic cells, and their 

 capacity at need to form any kind of tissue, he would 

 find it difficult to persist in his conception of the 

 " germ-plasm " as a machine-like mosaic of molecules. 



Sir Arthur compares the embryonic cells to an 

 army of workmen capable of various tasks whose 

 energies are co-ordinated to a common end — not by 

 a director but by hormones or chemical messengers 

 which they send to each other. I must frankly 

 confess that it baffles all my powers to conceive how, 

 from an unorganised mob of undifferentiated cells, an 

 organised structure could arise solely bv their mutual 

 influence. Certainly the amount of constructive 

 work accomplished in these circumstances by a crowd 

 of British workmen would be a minus quantity. 

 Surely the influence which organises and marshals 

 these cells must be one external to themselves. 

 There must, in the developing embryo, be some part 

 which takes the lead and emits the primary' hormones 

 which control the action of the rest. This I pointed 

 out in my address to Section D of the British Associa- 

 tion in 1916. May I illustrate this by an example 

 taken from a recent paper by Ruud and Spemann with 

 which Sir Arthur is possibly not acquainted ? If a 

 small portion of the developing nerve-plate of Triton 

 alpestris be grafted into the ectoderm of a gastrula 

 of Triton tcBniatus in a region where normally the 

 neural plate is not found, it will organise the ectoderm 

 cells around it into a neural plate, in the midst of 

 which it will be found, distinguishable from the cells 

 of the host by its different colour. 



Let me in conclusion suggest to Sir Arthur Keith 

 that these primary hormones or " formative stimuli," 

 which initiate development and give it its course, are 

 the physical correlates and bearers of the memories 

 of the race, stored in the egg-cell which has in turn 

 received them from the tissues of the parent genera- 

 tion. E. W. MacBride. 



As I read over the homily which my friend Prof. 

 MacBride has addressed to readers of Nature in 

 general and to myself in particular — one with which 

 we are all becoming familiar — I was reminded of an 



