246 



NA TURE 



[July 16, i ;o8 



The Form of Birds' Eggs. 



In Nature of June 4 (pp. 11 1-3), in a paper by Prof. 

 D'.^rcy Wentwortfi Thompson read before the Zoological 

 Society, April 28, the way in which form in birds' eggs 

 is to be accounted for is discussed. Referring to the 

 accepted causes of variation in form of eggs, Prof. Thomp- 

 son says : — " Whatever truth there be in these apparent 

 adaptations to existing circumstances, it is only by a very 

 hasty logic that we can accept them as a vera causa or 

 adequate explanation of the facts ; and it is obvious to 

 my mind that in attempting to deal with the forms assumed 

 by matter, whether in the organic or the inorganic world, 

 we ought first to attempt to deal on simple physical lines 

 with the forces to which it has been subjected, that is 

 10 say, the intrinsic forces of growth acting from within, 

 and the forces of tension and pressure that may have acted 

 from without." 



In other words, for the antecedent cause (adaptation to 

 surroundings) is substituted modification resulting there- 

 from or the consequential cause ; and far from it being 

 " very hasty logic " to assume the former, it is, to my 

 mind, hasty logic to rule it out and to substitute for it an 

 effect. In any case, the consequent is not a " vera causa 

 or adequate explanation," as must at once be apparent. 

 Again, force or energy determines the " forms assumed by 

 matter " ; and in a question of this kind we cannot com- 

 pare the inorganic and organic worlds, since in the latter 

 we find conscious effort and thought an attribute, so far 

 as we know, not applicable to the former, and in causa- 

 tion cither can play a very effective part. In regard to 

 adaptation to surroundings or influence of external con- 

 ditions, which to all is not meaningless, wc may state the 

 following premises : — 



(i) There is a distinct evolution in form from a spherical, 

 through various forms of ellipse, to the elongated conical 

 egg-shell of the guillemot cited. 



(2) In abnormal and embryonic eggs, normally non- 

 spherical, there is often a reversion to the spherical form. 



(3) Certain types of eggs characterise birds morphologic- 

 ally allied, addicted to the same mode of life, and subject 

 to the same incident physical surroundings. 



(4) Correlated with identity of form is unity of type in 

 coloration, and it seems reasonable to suppose that this 

 is due also to influence of surroundings — arising from which 

 adaptations, protective resemblance, &c., may become 

 necessary. 



(5) When an egg retains permanently a form that it 

 appears reasonable to regard as suited to environment, the 

 same type of egg is not usually found to characterise other 

 birds habituated to a different environment. 



From (5) and the preceding premises, even though partly 

 inferential, we may logically conclude that the form of 

 eggs is connected with environment, for experiment, 

 indeed, shows that all types of egg but that of the guille- 

 mot will roll off a table more readily than the latter, to 

 instance one case alone ; and it is generally admitted that 

 the most potent factor in the production of modifications 

 is the influence of environment. Furthermore, the egg- 

 shell is not an indispensable product of reproduction, but 

 has become necessary as a result of the acquired characters 

 of different species of terrestrial organisms, .so that we 

 may regard this as further evidence of the influence of 

 surroundings upon the bird and its egg ; and thus varia- 

 tion in nesting-site, contributing to variation in form of 

 egg, appears to follow by means of modifications arising 

 from the causes indicated. 



The determination of a force, in fact, is antecedent to 

 its consequential mode of action. The latter is surelv not 

 an efficient cause, but an effect of an antecedent which we 

 may call an eflScient cause if we like. The one is sub- 

 jective, the other objective, in nature, and these cannot 

 be substituted. Function in an organ, or mode in which 

 an organ performs its function, is not equivalent to cause. 

 On this and the influence of surroundings reference m.ay 

 be mride to the writings of Sir Ray Lankester 

 f" Embryology and Classification," pp. 36-q), on the in- 

 fluence of memory and energv in evolution. Prof. Cope 

 (Aiiier. Nat., .iS.Ss, pp. 454^0), Ribot (" Hereditv "), 

 Hyatt (" Bioplastology." pp. C0-S7), Herbert Spencer 

 (" Principles of Biology "). 



NO. 2020, VOL. 78] 



Whe'iher we regard the corpuscular or germ-plasm theory 

 as the only tenable one, or whether we favour the 

 dynamical theory, we can, I think, in either case allow 

 that memory persists ; and if it persists can it not recall 

 in answer to stimulus a response given by the ancestor of 

 a species? Cells may contain or retain by virtue of 

 memory the characters of the species, but effort or energy 

 is no doubt the means by which a response to stimuli, 

 causing new characters to arise (and become fi.xed), may 

 be conveyed. We may regard it as feasible that modifica- 

 tions are indirectly due to the influence of energy and 

 memory on the germ-plasm, the specific type preserver, 

 and that heredity or variation may be influenced in nature 

 by the "characters acquired by incidence of physical 

 surroundings, whilst a response in an organism to outside 

 stimuli creates a response from within, stimuli acting from 

 within and without reacting upon one another. An 

 organism being " a combination of rhythmically acting 

 parts in moving equilibrium," it follows that " a change 

 to a new state of equilibrium " will bring " the actions • 

 of all organs, reproductive included, into harmony with • 

 these actions," and the fact that " the units and the aggre- 

 gate must act and react upon each other " (Herbert 

 Spencer) more or less illustrates the view adopted. When 

 the influence of memory and energy, and the reactions they 

 give rise to, are duly appreciated, the recurrence during 

 successive generations of Identical characteristics is more 

 readily understood, and the action of pangenesis becomes 

 obscure if this excludes the perpetuation of all characters 

 arising during the phylogeny of the group or the history 

 of the individual. 



The validity of the mode in which eggs assume different 

 forms described by Prof. Thompson I freely admit, but 

 in claiming it, as he does, as a cause of their variation I 

 cannot agree with him, since mode of action follows deter- 

 mining cause, and, as Hyatt s.3ys, " The action of 

 physical causes takes effect upon an irritable plastic 

 organism which necessarily responds to external stimulant 

 by an internal reaction or effort." 



A. R. HoRWOOD. 



Leicester Corporation Museum, June 17. 



Lord Kelvin's Philosophy. 



There is one word in Sir Oliver Lodge's interesting 

 article, under the above heading, published in Nature 

 of July 2, to which I think some exception may reason- 

 ably be taken. In speaking of explanation in terms of 

 force and action-at-a-distance, or in terms of motion and 

 a continuous medium, Sir Oliver says that " To Lord 

 Kelvin it would appear that both solutions were equally 

 satisfactory, and that it was only a question of which was 

 the most tractable." It is the word "equally" which is 

 rather strong. He might indeed, as Sir Oliver savs, prefer 

 " to resort to the Boscovich doctrine ": but he would only 

 do so in virtue of the tractability of the process, leaving 

 aside for the time the question of the greater fundamentals. 

 It was not at all a question of philosophy. It was a 

 question only of the desirability of partial progress in 

 place of no progress. His philosophy was Newtonian, 

 postulating forces but reserving a medium. 



In attempted explanation of certain elastic qualities in 

 matter, he postulated a " simplest " Boscovichian system. 

 That failing, he adopted a " second-simplest " system. 

 Similarly, in attempted explanation of matter and energv, 

 he postulated a simplest foundation in his vortex theoi-y. 

 That failing, he would doubtless have gladly framed a 

 second-simplest foundation had he seen it to be possible. 

 He was content to wait, meanwhile continuing his attack 

 on the unknown along more presently promising lines. 



In a letter of date December i, 1905, referring to the 

 molecular (Boscovichian) theory of magnetism and the 

 " interesting truth " which it represents, he said " which 

 will be added to when we know the physical quality of 

 a molecular magnet and its relation to ether and to 

 torrents of electrions through ether." In this spirit he 

 was willing to wait for a knowledge of the physical qualitv 

 underlying any other Boscovichian figuration. 



W. Peddie. 



University College, Dundee, Julv S. . . 



