6i8 



NA TURE 



[Oct. 



18S8 



tween the trout which respectively inhabited the two ponds 

 ("British and Irish Salmonidte," pp. 226-27, 1887). Will any- 

 one undertake to affirm, after looking at the coloured plates, 

 that these changes must ne:e sarily have been due to selection? 

 Again, in a recent communication to the Field (]u\y 7), Mr. Day 

 gives an engraving of a remarkable variation which is taking 

 place in the gill-covers of trout which have been transported to 

 New Zealand, and there "turned down "under nature. Pre- 

 mising only that, although this is a change of structure, there is 

 110 more adaptive meaning to be found in it than in those 

 changes of colour above mentioned, 1 I will quote Mr. Day's 

 remarks upon the subject: "It will be interesting to watch 

 the changes occurring among these trout in their new home, 

 and to observe whether these serrations are continued or merely 

 temporary ; for if they should become developed with time 

 there would be still more reason for constituting them a new 

 species than now exists among the various European races ; 

 while, should trout with serrated preopercles and interopercles 

 be admitted as constituting a new species, we could now trace 

 the process of development from its commencement, and show 

 how such has been occasioned by transplanting our European 

 trout to the warmer waters of the Antipodes." 



Should it be objected that, as a matter of fact, the state of 

 matters anticipated by Mr. Day has not yet arrived, my answer 

 would be obvious— namely, supposing tha' such a state of matters 

 had arrived, could the fact be reasonably held to annihilate the 

 whole theory of natural selection ? Yet this is what such a fact 

 would necessarily do, if we hold it to be "a necessary conse- 

 quence of the theory " that every species which exists, exists in 

 virtue of having been "selected." If we have not here a re- 

 ductio ad absurdum, I do not know how one can ever hope to 

 apply that method. 



Of course I am not disputing that in general there is a very 

 great distinction between local varieties and good species in 

 respect of peculiar adaptive characters. In other words, I 

 have no doubt at all that probably the great majority of 

 of species have been originated by natural selection, either as 

 the sole cause or in association with other causes. But the alle- 

 gation which I am resisting is, that it follows as a necessary 

 consequence from the theory of selection itself that every species 

 must owe its origin to selection. And I have endeavoured to 

 show that this allegation admits of being reduced to an absurdity. 

 When Mr. Wallace, in the letter above referred to, expresses 

 dissent from Mr. Gulick's view that species are frequently origin- 

 ated by the influence of isolation alone, he adds : "If this is a 

 fact, it is a most important and fundamental fact, equal in its 

 far-reaching significance to natural selection itself ; I accordingly 

 read the paper with continual expectation of finding some evi- 

 dence of this momentous principle, but in vain." Now, sup- 

 posing that Mr. Wallace had found the evidence which would 

 have fully satisfied him, would he therefore have been logically 

 required to abandon his own great generalization? Would he 

 have been required to acknowledge, not only, as he says, a 

 principle "equal in its far-reaching significance to natural 

 selection itself," but a principle which altogether superseded that 

 of natural selection ? I say it is absurd to suppose that such 

 would have been the case, and yet it must necessarily have been 

 the case if it be "a necessary consequence" of his theory that 

 all (if any) species are originated by > election. 



It will be remembered that 1 am not arguing the biological 

 question whether, or how far, species exist which do not owe 

 their existence to selection ; I am arguing only the logical ques- 

 tion whether it is "a necessary consequence of the theory of 

 selection " that they cannot. And I now submit that it no 

 more follows from the selecion theory alone, that "every 

 v.iriety " which becomes " a species " does so "in consequence 

 of being in some one or more respects better adapted to its 

 surroundings than " its existing cmtemporaries, than it does that 

 every variety which becomes a variety does so for the same 

 reason. If the former statement is a statement of biological 

 fact (which, for my own part, I do not believe), the fact is one 

 lhat would stand to be proved inductively as a fact : it cannot 

 be made good by way of logical deduction "from the theory of 

 selection." 



1 In this connection, also, it is of great importance to remember lhat it is 

 only twenty years ago since the trout in question were sent to New Zealand, 

 and their fry liberated in the waters there ; f jT the most ardent upholder 

 of the theory of natural selection as the sole cause of specific transmutation 

 will scarcely maintain that twenty years is long enough for survival of the 

 fittest to effect a structural change of an "unknown " adaptive character in 

 a long-lived animal with all the waters of New Zealand to spread over. 



I have thus dealt with Mr. Huxley's criticism at some length, 

 because, although it has reference mainly to a matter of logical 

 definition, and in no way touches my own theory of " physio- 

 logical selection," it appears to me a matter of interest from a 

 dialectical point of view, and also because it does involve cer- 

 tain questions of considerable importance from a biological point 

 of view. Moreover, I object to being accused of misunder- 

 standing the theory of natural selection, merely because some 

 of my critics have not sufficiently c msidered what appears to 

 them a " paradoxical " way of regarding it. 



George J. Romanes. 



How Se?- Birds Dine. 

 As I have ascertained that the following fact is not well 

 known, I send you this account in the hope that it may be of 

 interest to naturalists and to the general public. Anyone who 

 lives in the Western Hebrides will have often watched on a 

 calm day the sea-birds feeding with noisy clamour in the sea- 

 lochs and about the numerous islands. This is especially the 

 case in August, when the shoals of small herring are very plenti- 

 ful. Some years ago, when in a sailing-boat off the west coast 

 of Mull, I caught with a hand-net a dishful of these small fry 

 as they swam along the surface of the water. Last year, noticing 

 from a steam-launch the birds congregated in great numbers at 

 one spot, the idea struck me to steam to the place and try to get 

 a share of the birds' repist. The idea was at once carried out. 



1 stood on the prow with landing-net in hand, and the launch 

 wa steered towards the birds. As we drew near, the banqueters 

 flew away with evident dissatisfaction at the interruption, a few 

 of the more greedy making their last hasty dives. In another 

 moment we were at the spot, and 1 saw, to my intense surprise, 

 about 2 feet under the surface, a large reddish-brown ball, 



2 to 3 feet in length and 2 feet in depth. I made a frantic 

 swoop with the net into the ball, and brought on deck half a 

 pailful of the sea-birds' dinner. LVen as we passed we could see 

 the great living ball sinking and breaking into pieces. 1 his 

 year J aid others have tried the same spot with great success. 

 Sometimes the ball has sunk too deep to be reached ; some- 

 times there was no ball to be seen ; but on the most successful 

 day I filled a pailful in three hauls. In September we saw no 

 ball, because, perhaps, the fish hid grown too large for the 

 birds to manage. As far as I can judge, the modus operandi is 

 carried out by the divers, who surround a shoal and hem them 

 in on all sides, so that the terrified fish huddle together in a 

 vain effort to escape inevitable destruction. The divers work 

 from below and other sea-birds feed from above ; and, as in 

 some cases after the birds had been at work for some time I saw 

 no ball, I suppose not one fish is left to tell the tale. I must 

 leave to naturalists the real explanation of the matter ; but I 

 may mention that, when disturbed by the boat, the divers seem 

 to come to the surface in a great ring round the scene of their 

 feast. I may aho mention that once, when the boat was still 

 300 or 400 yards away, the birds suddenly rose and whirled 

 about with frightened screams. I wondered what could be the 

 cause, until I saw the round back of a porpoise rolling lazily 

 round at the exact spot, and then rolling back again. When 

 we steamed past there was no sign of a ball. What two delicious 

 mouthfuls for the porpoise ! Comtton. 



Loch Luichart, Ross-shire, N.B. 



The Zodiacal Light. 



Mr. O. T. Sherman gives an in'eresting communication or 

 the zodiacal light in Nature of Octo er 18 (p. 594), and asks 

 for reference to any observations. He alludes to Cassini. 

 The following extract from a letter by Cassini may not have 

 come under his notice: "It is a remarkable circumstance that 

 since the end of the year 1688, when this light began to grow 

 fainter, spots should have no longer appeared on the sun, whilt 

 in the preceding years they were very frequent, which seems tr 

 support, in a manner, the conjecture that the light may ari-t 

 from the same emanations as the spots and faculrc of the sun." 

 This does not quite tally with Mr. Sherman's notion that the 

 maxima of the zodiacal light coincide with the minima of sun- 

 spots. May it not rather be that, supposing sun-spots to be 

 largely occasioned by increased influx of meteoric matter falling 

 into the sun, which matter gets sublimed and repulsed to aug- 

 ment the materials forming the zodiacal light, therefore the 

 maxima of the latter may then lag behind the maxima of the 

 sun-spots. Henry Muirhead. 



Cambuslang, October 20. 



