58o 



NATURE 



[April 24, 1 8"' 



I do not believe that we are necessitated by the far sea flight of 

 birds, to assume a sixth sense. Is it not conceivable that birds 

 are capable of keeping exactly the same direction of flight for 

 many hours together, and so to fly somewhat like a shot ball or 

 a steamship with rudder bound fast ? From the physiological 

 side, it might of course be objected that a very slight difference 

 in the strength of the right and left wing-beats must cause a de- 

 flection from the original course, just as in the case of rowing 

 without a steersman, a constant control by sight is necessary, if 

 the right direction is not to be lost. To this might be replied, 

 however, that birds are so accomplished in flight, and that we 

 may assume they have an extremely fine muscular sense. Besides, 

 they migrate mostly in company, and an error in flight of one 

 bird will be easily corrected by the others. 



But how do they hit the direction in flying away from the 

 coast? They must be able to exactly measure the angle at 

 which they ought to leave the land. Therein, of course, a qviite 

 small error \\'ould involve great deflections from the proper 

 course, but do we know that this does not actually occur often 

 enough ? and may it not be supposed that in many cases corrections 

 are made in the flight, as soon as any point of orientation again 

 emerges in the circle of vision ? So much we at least know, that 

 even on land birds wander not infrequently. And it is at least 

 not demonstrated in any one of tJie cases cited by Mr. Newton, 

 that the birds referred to appeared on those islands every year, 

 nearly at the same time and in the same number. 



Mr. Newton adduces a second series of "facts" which seem 

 to be against the sufficiency of the five senses ; but are these really 

 facts ? 



The young, scarcely three months old, of many of our birds, 

 are said to pursue their flight southwards in autumn alone. Is 

 that certain ? and have we not here, perhaps, a too ready deduc- 

 tion of general niles from a few well-observed cases? Mr. 

 Newton even says : " This seems to happen with nearly all the 

 accipitres," &c. He quotes a letter from M. Giitke, stating that 

 in July "Young starlings pass over Heligoland by hundreds of 

 thousands without a single old bird accompanying them." I 

 confess that I cannot regard this as a fact, but as a more or less 

 probable conjecture; for M. Gatke, though an excellent ornitho- 

 logist could not possibly have inspected a hundredth part of 

 tliese'" hundreds of thousands " of starlings flying about. 



I do not mean to assert that these or the other data are false ; 

 they may well be correct. I merely hold that we must guard 

 a<^ainst building far-reaching theoretical inferences on obser- 

 vations the general validity of which is not in the least demon- 

 strated. 



But even supposing that all these data are correct ; further, 

 supposing it certain, that these young birds, which go forth 

 alone, also actually find the route of the species with the same 

 certainty as if they had known it long before, would these facts 

 be explained by the supposition of a magnetic sense ? I think 

 not. For in that case, what must have been born with the young 

 bhd? Merely this magnetic sense? i.e., the power of directly 

 perceiving external d rection in its own body? By no means. 

 There must also be born with the young bird the consciousness of 

 what angle to the magnetic meridian it must shape its flight at. 



But much more than this. It has been long known that birds, 

 so long as they are migrating over land, frequently alter their 

 direction ; hence, supposing the young bird to be guided by a 

 mao-netic sense, there must be born with it the tendency to fly 

 (say) twenty miles at an angle of 45° to the magnetic meridian, 

 then 100 miles at an angle of 27°, and so on. That this is a 

 physiological absurdity, no one would deny. 



For these reasons I hold that a special sense for direction does not 

 exist in birds, and that the phenomena of migration, however 

 wonderful they appear, yet cannot ultimately depend on magic 

 (Zauberei), and in this Mr. Newton no doubt agrees with me. 

 Hence, nothing remains but to try to explain these phenomena 

 by the known physical and mental properties of birds ; for there 

 is no third course. , . , ,, 



I shall be rejoiced if Mr. Newton succeed with this better 

 ^j^j^Q j^ August Weismann 



Freiburg im Breisgau, March 31 



The editor having afforded me the opportunity of seeing the 

 foregoing remarks, it will, perhaps, be convenient to the readers 

 of Nature that I should here add the comments I have to 

 make upon them. 



I deeply regret if my criticism of Dr. Weismann s treatise or 



lecture be open to the charge of unfairness. I had no wish to 

 misrepresent him, and I cannot see that I have been guilty of 

 such an act — indeed, the -wide publication of his theory would 

 render any attempt to do so futile. As to his acceptance of Dr. 

 Palmen's conjecture for "absolute truths," I must urge that he 

 took no exception to any of them, while, in the case of his 

 Bernacle or Brent Goose, he especially adopted (p. 27) that route 

 X which I had particular reason to consider unfounded. I did 

 not assert that Dr. Weismann spoke of birds flying over the sea 

 at the height of 20,000 feet, though there seems no reason why 

 some might not, if they can do so over the land ; nor did I 

 impute to him that they always keep land in sight. I had no 

 need to declare my disbelief in Dr. von Middendorft's magnetic 

 hypothesis, for I never met with any man that held it. I had 

 spoken of it already elsewhere (E7icycl. Brit. Ed. 9, iii., p. ^(><)), 

 and I considered it had been set at rest for ever by Prof. Baird in 

 the article I cited. In like manner it seemed useless to disclaim 

 any belief in the possession by birds of a "sixth sense" which 

 is not common to ourselves and other animals. My only object 

 was to show that Dr, Weismann's theory was inconsistent with 

 certain facts, and nothing he has since adduced makes me think 

 it otherwise. As to some of these "facts "he is incredulous, 

 and I have no fault to find with his caution in this respect, but I 

 am sure that the more he investigates them, the less he will be 

 inclined to demur to them. I shall leave to the ornithologists of 

 New Zealand the defence of those that relate to their cuckoos. Dr. 

 Weismann will find in Mr. Jones's "Naturalist in Bermuda" 

 (London, 1859) more than enough to justify my allegations in 

 regard to the passage of Charadrius vir^itiicus (not Uuvialis) 

 over those islands ; indeed^it has long been notorious ; and as to 

 the plovers of the Sandwich group, I have not only to thank 

 Capt. Long, R.N., for his confirmation {supra, p. 460) of my 

 statements, but also Prof. George Forbes, who kindly informs 

 me that when there, on the occasion of the transit of Venus, he 

 shot scores of these birds, and that his friend Capt. Cator, R.N., 

 of H.M.S. Scout, having sailed thence, was overtaken in mid- 

 ocean by them, flying in a direct line for Vancouver's Island, on 

 arriving at which he found they had already reached it. Con- 

 cerning the "facts" relating to some young birds preceding their 

 parents in migration, the more inquiries I make of well-placed 

 observers the more satisfactory are the answers. For want of 

 space I cannot here give the details, but I may just say that Mr. 

 Cordeaux, who has been for many years a watchful observer of 

 migratory birds on the Lincolnshire coast, has named to me nine 

 species of Lif/ticolcr, of which he has personally assured himself 

 that the young migrate apart from, and invariably arrive earlier 

 than, the old— thus fully bearing out Temminck's assertion, made 

 nearly forty years ago. The case of our cuckoo-, which 1 cited, 

 is incontestable, and M. Gatke, I doubt. not, will satisfy any 

 scruples about his starlings in that book which we are expecting 

 from his hands. • , 



I will also take this opportunity of replying to Mr, Pringle s 

 note {supra, p. 481). My chief reason for not referring to the 

 matter of temperature was that we know too little of the power 

 of birds to resist extreme cold to depend much upon it, and I 

 thought I would not take up room by bringing in that question. 

 Doubtless there is something in what he says touching the loom 

 of land, but I fail to see how it will help very far, and especially 

 in nocturnal flights. Alfred Newton 



Magdalene College, Cambridge, April 20 



Colour in Nature 



I WISH to offer a few remarks upon Mr. Wallace's kind and 

 appreciative review of my work on the " Colour-Sen^e' in 

 Nature, vol. xix. p. 501. Mr. Wallace attributes to me 

 "many errors " and inaccuracy as to matters of fact ; but I do 

 not think the instances he alleges are sufficient t justify the 

 statement. Had I said in every case what Mr. Wallace makes 

 me say, I should, doubtless, have been misrepresenting facts ; 

 but it seems to me that in most of the passages to which he refers 

 he has slightly misconceived my meaning. I should not attempt 

 to oppose so distinguished a naturalist on points of biological 

 inference, but I venture to defend the accuracy of my statements 

 of fact. . ., ,, 



I. " Scissirostrum Pagei does not ' belong to a family generally 

 dull,' while it is itself decidedly dull-coloured. Ihe hr^t 



statement will be correct if we ^Xz-cs: Scissirostrum among the 

 brilliant starlings ; but Mr. WaUace himself, following Prince 



