March 



1885] 



NA TURE 



43; 



How Thought Presents Itself among the Phenomena 

 of Nature 



In your paper of the 5th you give a short abstract of a recent 

 lecture at the Royal Institution by Mr. G. Johnstone Stoney, on 

 the question "How Thought presents itself among the Pheno- 

 mena of Nature. " In this abstract I observe an assertion which 

 is quite new to me, and, I must add, quite unintelligible. It 

 occurs in the first paragraph. The assertion seems to be that 

 there is an absolute distinction between molar and molecular 

 motion, inasmuch as that, in the case of molecular motion there 

 is no authority for the conviction that there must be some 

 "thing" to be moved. The conception of motion involves the 

 conception of matter as a necessary or inseparable concomitant — 

 although the abstract idea of motion may, in a sense, be sepa- 

 rately entertained. Is there any difference in this respect between 

 molar and molecular motion ? A molecule is a group of atoms, 

 and an atom is only conceivable as an ultimate particle of 

 matter. I hope that some further explanation may be given upon 

 this point, which is one of the highest interest and importance, 

 both as a matter of physical and of metaphysical speculation. 



Inverary, March 8 Argyll 



The Compound Vision and Morphology of the Eye 

 in Insects 



Mk. SYDNEY HlCKSON, in your issue of February 12 (p. 341), 

 makes certain statements concerning my paper in the Trans- 

 actions of the I.innean Society on this subject. I will not follow 

 Mr. Hickson through his entire article, as I conceive it is suffi- 

 ciently refuted by my paper itself. He says : " It would be 

 tedious to bring evidence of this kind to confirm a theory which 

 is already fully established." I would ask Mr. Hickson if any- 

 one can explain the vision of the compound eye intelligibly on 

 the received theory ? I would also remind your readers that 

 Prof. Huxley, writing of the crayfish in 1880, accepted the view 

 with extreme caution ; he said, " The exact mode of connection 

 of the nerve fibres with the visual rods is not certainly made out ; " 

 that Claparede never accepted it, and Max Schultze admitted 

 that there were grave physical difficulties in the way of its 

 acceptance. 



Mr. Hickson is very anxious, apparently, to deny me what I 

 never claimed — i.e. the discovery of a layer of definite structure 

 beneath the basilar membrane. What I do c'aim is the dis- 

 covery of the nature of its elements. I deny, in my paper, that 

 the optic nerve passes through these structures, and I deny that 

 these consist of a fine reticulum of nerve-fibres. These are 

 questions of fact and observation, not of theory or deduction. 

 If I am wrong, I am wrong. But the way to test my work is by 

 working out the eye as I have worked it out. I have spent 

 nearly ten years in this work, and I do not expect to have my 

 views generally accepted for another ten years. 



The absence of pigment and retinal purple is a secondary- 

 question. I do not know, nor does any one know, whether 

 there be retinal purple or not in this layer. I admit that pig- 

 ment is absent in the retina (my retina) of some insects and 

 crustaceans, and I have recorded the fact. I am not yet con- 

 vinced that we can say vision is impossible without it. Albinos 

 have vision undoubtedly in the absence of retinal pigment. He 

 would be a bold man who asserted that vision could not be 

 effected without pigment in the retinal region. The colourless 

 collodion film of the photographer is affected ; why not retinal 

 rods? Here, again, it is a question of fact, not theory. 



The presence of pigment proves nothing with regard to the 

 function of the great rods, any more than it shows that the iris 

 of a vertebrate is sensitive to light. 



The absence of my retinal layer in Periplaneta and Nepa is 

 imaginary on the part of my critic, for I have examined it care- 

 fully in both, and I figure the elements from the former. I 

 maintain that the same structures exist in all the Crustacea, 

 although they are short and more difficult to demonstrate. 



Again, in the morphological question my views are not fairly- 

 stated by Mr. Hickson. I admit his facts, but deny his deduc- 

 tions. The hypodermis forms the dioptric structures, as the 

 epidermis of the vertebrate forms the lens ; my contention is 

 that the retina in the insect, like the same structure in the Verte- 

 brata, is developed as an outgrowth from the nervous systi m. 



Benjamin Thompson Lowne 

 65, Cambridge Gardens, Notting Hill, W., February 23 



I do not wish to undertake a lengthy controversy with Mr. 

 Lowne on the question of the retina of insects, but I cannot 

 retrain from making a few remarks on the letter you publish 

 above. 



I am afraid Mr. Lowne has misunderstood my criticism when 

 he asks me " If any one can explain the vision of the compound 

 eye intelligibly on the received theory ? " My criticism was not 

 meant for any theory of pure optics, but for the theory that the 

 retihulae are not the true nerve-end cells. 



Mr. Lowne's statement that albinos are devoid of retinal pig- 

 ment, is not strictly accurate, for Kiihne pointed out, and any 

 one can see for himself, that all albino rabbits and other verte- 

 brates possess a true retina purple. Moreover, the rods of 

 Cephalopods and of Pecten, which seem to be devoid of pigment 

 in spirit specimens, possess, as Hensen has pointed out, a true 

 retina purple. In fact, I know of no exception to the rule I 

 laid down — namely, that optic nerve-end cells are pigmented, 

 and I should be glad if any of your readers could point out any 

 exceptions to it. 



Mr. Lowne's reiterated statement that the optic nerve fibrils 

 do not end in the retinulse is, as I said, contrary to my own 

 observations. I have submitted my preparations to several 

 eminent naturalists, who agree with me in my account of their 

 distribution. I shall be happy to submit them to any others 

 who may feel interested in this matter. 



The other statements in my notice which Mr. Lowne contro- 

 verts I will not refer to again here, as they will be fully ex- 

 plained and illustrated in my forthcoming paper in the Quarterly 

 Journal of Microscopical Science, the proof-sheets of which I 

 have now in hand. Sydney J. Hickson 



Anatomical Department, Museum, Oxford, February 25 



Civilisation and Eyesight 



In connection with Lord Rayleigh's letter in Nature, p. 

 340, on the above subject, I venture to hope that the following 

 may be of interest : — 



In the "Expression of the Emotions" the late Mr. Darwin 

 quotes some observations — if I recollect correctly — by Gratiolet 

 tending to show that, under the influence of fear, the pupils of 

 animals' eyes dilate. Observations extending over some years 

 have convinced me that fear is undoubtedly capable of thus 

 causing dilation of the pupils (see Dr. Hack Tuke, " Influence 

 of the Mind on the Body ") ; and in general literature, such as 

 travels, novels, &c, I have met with many instances in which 

 the eyes of both men and animals under this condition have been 

 so described by the writers. 



Is dilation of the pupil under the influence of fear to be 

 explained on the assumption that the increased aperture of the 

 eye enables a more effective scrutiny of the object causing terror, 

 and has thus been of service in the struggle for existence ? 



An answer to this question is not ea^>y to give, for, although 

 dilation of the pupil under the influence of fear may have 

 originally been of direct service to an animal, yet this condition 

 may in time have come to be associated with other emotions in 

 which it is not so easy to trace any such direct benefit. 



Observations upon the subject are by no means easy (varying 

 light, for instance, varies the aperture of the eye), but in the 

 course of my observations I became much inclined to believe 

 that other strong mental emotions besides fear [e.g., joy or plea- 

 sure) may be capable of giving rise to dilated pupils. 



Charlotte Bronte, in "Jane Eyre," is one of the only writers 

 who associates a dilated pupil with other emotions than fear. 

 Here is the sentence : — "Pain, shame, ire, impatience, disgust, 

 detestation, seemed momentarily to hold a quivering conflict in 

 the large pupil dilating under his ebon brow." 



It is to be feared that the experimental investigation of eye- 

 sight with artificially contracted or dilated pupils is scarcely 

 practicable, for drugs, such as atropine or eserine, act not only 

 on the pupil, but also on the power of accommodation for 

 distance. J. W. CLARK 



Liverpool, February 21 



P.S.— I see Dr. M. Foster, in his "Text-Book of Physio- 

 Jogy," mentions the dilation or contraction of the pupil which 

 attends the adjustment of the eye for distant or near objects 

 respectively, and also its dilation "as an effect of emotions." It 

 thus seems highly probable that strong and very different mental 

 emotions may give rise to dilated pupil. Dr. Herdman has 

 suggested to me, as an explanation of this, that an intens 



