488 



NATURE 



\_March 27, 1890 



dwindling and ultimate loss of the organ. I would, however, 

 venture to supplement what he has said by the following : viz., 

 given the state of panmixia, it is apparent that variations in the 

 direction of excessive size will be injurious — both as taxing 

 the nutriment of the organism, and often as mechanical en- 

 cumbrance. On the other hand, variations in the direction 

 of greatly diminished size will be advantageous, as causing 

 a diminished tax on the resources of the organism. Now 

 it is a demonstrable fact that excessive variations in both direc- 

 tions do naturally though rarely occur — probably more often than 

 is supposed, since we do not see all the young born. If the varia- 

 tions in the direction of excessive diminution of a useless organ 

 (as, for instance, tailless cats or hornless sheep) survive as being 

 less taxed — whilst the complementary variations in the direction 

 of excessive size tend in the struggle to die without reproducing, 

 owing to their awkwardness and their relatively greater burden 

 in life —then it is clear that panmixia may lead rapidly to the 

 dwindling and eventual extinction of a disused organ without 

 any transmission of acquired parental character. The fact that 

 there is no use for an organ — or, in other words, the " effect of 

 disuse" — is that the congenitally small varieties of the organ 

 survive, and are even favoured in the struggle for existence. 



Whilst Weismann has the merit of having insisted on a form of 

 his doctrine as the effective reply to those who argue in favour of 

 Lamarck's theory of the transmission of acquired qualities from 

 instances of " disuse," it is yet the fact that Mr. Darwin him- 

 self recognized and formulated the doctrine of panmixia in the 

 last (sixth) edition of the "Origin of Species, "published in 1872 ; 

 and he even went further than Weismann, for he associated the 

 principle of the economy of material with the principle of the 

 cessation of selection. It is therefore, it seems to me, not at all 

 improbable that when Darwin refers, here and there throughout 

 his works, to a reduced or rudimentary condition of an organ as 

 " due to disuse," or " explained by the effects of disuse," he does 

 not necessarily mean such effects as the Lamarckian second law 

 asserted and assumed (though often he does appear to mean such) ; 

 but he may mean, and probably had in his mind, the effects 

 of disuse as worked out through panmixia and economy of 

 growth. 



The passages in Darwin which seem to me to have been 

 missed or neglected by those who think panmixia altogether a 

 new idea are as follows : — 



(1) "If under changed conditions of life a structure before 

 useful, becomes less useful, its diminution will be favoured 

 for it will profit the individual not to have its nutriment 

 wasted in building up a useless structure." After an example 

 in point from the group of the Cirripedia, Darwin con- 

 ttinues ; "Thus, as I believe, natural selection will tend in the 

 long run to reduce any part of the organization as soon as it 

 becomes, through changed habits, superfluous, without by any 

 means causing some other part to be largely developed in a 

 corresponding degree" ("Origin of Species," sixth edition, 

 p. 118). 



(2) " Organs, originally formed by the aid of natural selection, 

 when rendered useless, may well be variable, for their variations 

 can no longer be checked by natural selection. ... It is 

 scarcely possible that disuse can go on producing any further 

 effect after the organ has once been rendered functionless. 

 Some additional explanation is here requisite, which I cannot 

 give. If, for instance, it could be proved that every part of the 

 organization tends to vary in a greater degree towards diminu- 

 tion than towards augmentation of size, then we should be able 

 to understand how an organ which has become useless would 

 be rendered, independently of the effects of disuse, rudimentary, 

 and would at last be wholly suppressed ; for the variations 

 towards diminished size would no longer be checked by natural 

 selection. The principle of the economy of growth explained in 

 a former chapter [cited in quotation No. i], by which the 

 materials forming any part, if not useful to the possessor, are 

 saved as far as possible, will perhaps come into play in rendering 

 a useless part rudimentary " ("Origin of Species," sixth edition, 

 pp. 401-402), 



I had written thus far, and intended to finish this letter by 

 asking if the anti-Lamarckians are not really carrying out the 

 spirit of Darwin's doctrines, although not the absolute letter, 

 when I received your issue of March 13, containing a long letter 

 from Mr. George Romanes, headed "Panmixia." In that letter 

 Mr. Romanes, whilst amending (as I have done above) Prof. 

 Weismann's statement of the principle of panmixia, makes the 

 definite assertion that " it is remarkably strange that thisi prin- 

 ciple should have been overlooked by Mr. Darwin." 



Probably your readers will be as much astonished as I waS 

 when they read the extracts I have above given from the " Origin 

 of Species " by the side of Mr. Romanes's letter. 



After dismissing Mr. Darwin, Mr. Romanes proceeds to say: 

 " In this connection, however, it requires to be stated that the 

 idea first of all occurred to myself, unfortunately just after the 

 appearance of his last edition of the 'Origin of Species.'" 



Now, inasmuch as the idea in question is (as I have shown 

 above) formulated in the last edition of the " Origin of Species," 

 I confess that I do not think it requires to be stated that the 

 idea occurred to Mr. Romanes shortly after the publication of 

 that work. What more natural? The idea occurred to me 

 also shortly after the passages above quoted from Mr. Darwin 

 were published. It certainly never appeared to me "unfor- 

 tunate " that this was the case, and I cannot see where the mis- 

 fortune comes in in regard to Mr. Romanes. As soon as the 

 matter had taken root in his mind, Mr. Romanes published in 

 Nature, March 12, April 7, and July 2, 1874, an exposition of 

 the importance of the principle of cessation of selection as a 

 commentary upon a letter by Mr. Darwin himself (Nature, 

 vol. viii. pp. 432, 505) in which Mr. Darwin had suggested that, 

 with organisms subjected to unfavourable conditions, all the 

 parts would tend towards reduction. Mr. Darwin, with his usual 

 kindly manner towards the suggestions of a young writer, gives at 

 p. 309 of vol. ii. of " Animals and Plants under Domestication " 

 (second edition), Mr. Romanes's view, " as far as it can be given 

 in a few words.'* The view, as it there appears in Mr. Darwin's 

 words, is certainly not the same as that which Mr. Romanes has 

 expounded in Nature of March 13, 1890 (p. 437), and since it 

 represents what Mr. Darwin had been able to gather from Mr. 

 Romanes's letters to Nature of 1874, it is not at all surprising 

 that Mr. Darwin did not recognize any resemblance between it 

 and his own statement, viz. that " the materials forming any 

 part, if not useful to the possessor, are saved as far as possible, " 

 thus " rendering a useless part rudimentary." Whether this 

 is, or was, Mr. Romanes's view or not, it is Darwin's, and is the 

 essence of the anti-Lamarckian view of the effects of disuse. 



March 15. E. Ray Lankester. 



Exact Thermometry. 



Shortly after the publication of my second letter on this 

 subject (Nature, January 23, p. 271) I received a letter from 

 M. Guillaume, who very kindly called my attention to a paper 

 by Prof J. M. Crafts {Comptes rendtis, xci. p. 370), in which 

 the "plastic theory " is discussed. Prof Crafts states that he 

 has subjected thermometers to prolonged heating at 355° C, 

 under various conditions as regards pressure, the internal pres- 

 sure being in many cases considerably greater than the external, 

 but that there was invariably a rise of the zero-point. The ex- 

 periments were carried out in very much the same manner as 

 that described in my first letter (Nature, December 19, 1889, 

 p. 152), and had I known at the time of the earlier work of 

 Prof. Crafts, I should of course have referred to it. Prof Crafts 

 also describes and quotes experiments with air-thermometers, 

 the temperature in one determination by Regnault being as high 

 as 511° C, and the internal greater than the external pressure ; 

 in every case the bulb diminished in volume. From these re- 

 sults, Prof Crafts concludes that it is not proved that pressure 

 plays any part in the contraction of the glass. 



My experiments can therefore be regarded as little more than 

 confirmatory of the earlier work of Prof Crafts and others, but 

 as such it may be worth while to give the results. The method 

 adopted was fully described in my first letter, and it is therefore 

 only necessary to repeat that in thermometer A the external 

 pressure exceeded the internal, while in thermometer C there 

 was considerable internal pressure, but no external. According 

 to the plastic theory, therefore, the zero-point of A should have 

 risen, while that of C should have fallen. The results previously 

 described were regarded as insufficient by Prof Mills, and I 

 have therefore continued the heating for a much longer time. 



I have also made similar experiments with two other thermo- 

 meters belonging to the same batch, at a temperature of about 

 356°, the thermometers being heated in the vapour of boiling 

 mercury. During the first three hours, the two thermometers 

 a and b were treated in precisely the same manner, as regards 

 pressure, as A and C, and it will be seen that the zero-point of 

 b showed a slightly greater rise than that of a. Afterwards, air 

 was admitted into thermometer a, so that there was an excess of 

 internal over external pressure in both thermometers, but the 

 excess was greater by one atmosphere in b than in a. 



