August 1 1, 1887] 



NATURE 



341 



Thus we may say, in very young AmmoccEtes the parietal eye 

 possesses black pigment, in older Ammocoetes white pigment, 

 and in adult Petromyzon there is a reversion to black pigment. 

 In what relationship these three pigments stand to each other I 

 am unable to say. 



The last point concerns the hypotheses as to the origin of the 

 eye. These were really two in number. The first of them — that 

 which derives the paired eyes and the parietal eye from one 

 common dorsal sense-plate — I hold to be fairly certain, and, 

 indeed, there are many facts to support it. 



The second, which derives the parietal eye as a later 

 involution of a portion of this same plate, an involution 

 which was supposed to have taken place after that of the 

 paired eye " Anlage," I only believe to be conceivable. My 

 hope of establishing it lay in the verification of an observation of 

 Goette's ; there are no facts to support it, and from more recent 

 investigations of the development I am disposed to attach less 

 value to it. For, from these developmental researches, from 

 studies of the types of eye presented by vertebrates and some 

 invertebrates, and lastly, but not least, from valuable discussion 

 with and criticism by Prof. Wiedersheim, a new track has been 

 found, which gives the explanation of a good deal, but the 

 problem is too long and complicated for treatment here. 



The first hypothesis mentioned above is taken as the starting- 

 p int, but for the further details there are several other questions 

 which have first to be solved. J. Beard. 



Anatomisches Institut, Freiburg i/Br., July 20. 



Physiological Selection. 



Like so many others who have written on this subject, Mr. 

 Rusden freely criticises my views without having deemed it 

 desirable to read my paper. Had he taken the trouble to do 

 so, he would have found a sufficient recognition of the general 

 fact that instinctive habits not unfrequently serve to mitigate the 

 swamping effects on incipient varieties of intercrossing with their 

 parent forms. Moreover, he would have found that there are 

 others of these habits mentioned by me which are probably 

 much more effectual in this respect than is the one to which he 

 draws attention. Nevertheless, it appears to me evident that 

 all these habits taken together cannot count for much, even 

 where they occur; while it is unquestionable that they occur 

 only in a very small fractional part of organic nature considered 

 as a whole — namely, in some among the more intelligent species 

 of animals. The whole of the vegetable kingdom, an immense 

 majority of the Invertebrata, and a considerable majority of the 

 Vertebrata, cannot possibly have had any of their specific differ- 

 entiations influenced by any of these forms of what 1 have already 

 designated as "psychological selection." This sufficiently 

 obvious consideration appears to have entirely escaped Mr. 

 Rusden. He adduces a well-known and a comparatively limited 

 form of psychological selection as a "simple solution " of the 

 di.fficulty from free intercrossing in all cases ! 



The other parts of his letter merely indorse the views which 

 are published in my paper. I there say that the theory of 

 natural selection is not, strictly speaking, a theory of the origin of 

 species, but a theory of the development of adaptations. Having 

 read this statement, your correspondent writes : — "To consider 

 the theory of natural selection as a theory of the origin of species 

 is, therefore, clearly an error. • . . The theory of natural selec- 

 tion is one, not of the origin of species at all, but of the preser- 

 vation of particular varieties," i.e. those which present an 

 adaptive character. I do not see how his agreement with 

 my views in this matter could be more clearly expressed, and 

 therefore I cannot understand why he supposes that he is here 

 criticising anything which I have written. If the point of his 

 criticism is that I imagine Mr. Darwin to have fallen into the 

 error of regarding the theory of natural selection as (primarily) a 

 theory of the origin of species, this would merely show again 

 that he has not read my paper. My contention from the first 

 has been that upon this point I am in full agreement with Mr. 

 Darwin, and differ only from those Darwinians who differ from 

 their master in holding that all specific changes are likewise 

 adaptive changes, and vice versd. It is only in the presence of 

 this non-Darwinian assumption that specific changes and 

 adaptive changes become synonymous terms, with the conse- 

 quence that the theory of natural selection is to be regarded as 

 in all cases the only theory of the origin of species. 



And this leads me to the last point in my critic's letter. I 



have argued that the above-mentioned non-Darwinian assump- 

 tion is opposed to observable fact, seeing that " in a large pro- 

 portional number of cases" specific characters appear to be 

 wholly useless. Nothing has surprised me so much on the part 

 of my critics as to have found this statement vehemently chal- 

 lenged by so accomplished a naturalist as Mr. Wallace, and 

 therefore I am now engaged in collecting a quantity of evidence 

 upon the subject. But the point here is that Mr. Rusden 

 appears to think there is some ambiguity attaching to the terms 

 "use" and "utility." For he asks whether these words have 

 " any real significance outside human interests and considera- 

 tions." Now, I can scarcely understand how anyone at this 

 time of day could suppose that when these words are employed 

 in their Darwinian sense they are intended to have any reference 

 to human interests. When an evolutionist speaks of the utility 

 of an organ, it is hardly conceivable that anyone should under- 

 stand him to mean anything else than the utility of that organ 

 to the species which presents it. Therefore, the term " utility" 

 is equivalent to the term "adaptation," and to say that any 

 organ or structure is of use is one and the same thing as to 

 say that it is adapted to the performance of a function which 

 is of benefit to the organism or to its species. Such, at any 

 rate, is the only sense in which I have myself employed these 

 words ; and in doing so I have, of course, followed the 

 terminology of Mr. Darwin, as my critic might have observed 

 without going beyond one of the quotations which he himself 

 makes from the "Origin of Species" — namely, " I have called 

 this principle by which each slight variation, if useful, is pre- 

 served by the term ' natural selection. ' " 



George J. Romanes. 

 Geanies, Ross-shire, N.B., July 29. 



The Droseras. 



Miss Anne Pratt in her " Wild Flowers," vol. ii. p. 155, in 

 describing the three British species, after stating the character 

 of the stems and flowers, remarks, "but many persons who 

 know the plant well have never seen the flowers fully open." 

 Two of the species, D. rotundifolia and D. longifolia, are found 

 in a bog on a common near here, and these have lately flowered 

 in captivity. They were transferred from their habitat and 

 placed in a large saucer with peat and Sphagnum, under a bell 

 glass. The flowers have expanded from 10 a.m. to noon each 

 day, after which the sun left them. A D. longifolia in another 

 position was seen to flower at 2 p.m. Moisture and sun seem 

 the conditions to bring out the blossoms. I am not aware 

 whether they have flowered in situ, as my plants were gathered 

 in the early morning. 



Ramondia pyrenaica, brought from Bagneres de Luchon ten 

 years ago, has flowered each year on an outside rockery in my 

 garden. J. Rand Capron. 



Guildown, Guildford, July 28. 



Comrades. 



My children and their governess, when staying in the north of 

 Ireland lately, witnessed the following curious display of feeling, 

 in animals not usually credited with feelings. A boar pig was 

 in the habit every morning of going to the basket where a blind 

 kitten of about six weeks old was kept, allowing the little thing 

 to creep on to his back, and then taking it about and caring for 

 it during the day. The kitten got its food at the same time as 

 the pig, and at the same trough. In the evening the man who 

 saw to the animals used to carry the kitten back to its basket to 

 pass the night. " Oil done la vertu va-t-elle se nicher ? " 



Pollokshields, Glasgow, August i. E. R. 



D 



A NEW COSMOGONY} 

 II. 



R. BRAUN has earned by his excellent series of 

 — observations on sunspots (Nature, vol. xxxy. p. 

 227) a title to be heard with particular respect on subjects 

 connected with solar physics. In unfolding his views 



' " Ueber Cosmogonie vom Standpunkt christUcher Wissenschaft. Mit 

 finer Theorie der Sonne." Von Carl Braun, S.J. (Miinster : Aschendorff, 

 1887.) Continued from p. 323. 



