n^ 



NATURE 



[August i8, 192 i 



Letters to the Editor. 



yihe Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications .] 



Biological Terminology. 



Actually we are now talking about biological 

 method. In his last letter (Nature, July 28, p. 680) 

 Sir Archdall Reid makes three appeals to me. My 

 own contribution to the discussion has been confined 

 to a defence of systematic biology, and I have no 

 authority to answer for any " sect of biologists." But 

 surely most of us accept the principles of scientific 

 work that he lays down ; most of us realise that our 

 interpretations are mere working hypotheses ; and 

 most of us are always on the look-out by observation or 

 experiment for those crucial facts which shall confirm 

 or upset our hypotheses. My own difficulty has been 

 either to devise a question that should be universally 

 accepted as crucial, or, having devised one, to elicit 

 the relevant facts. Biologists who can experiment 

 with their material are certainly in a better position 

 to perform both these operations than is one who can 

 only observe portions of extinct animals. The distin- 

 guished author whom Sir Archdall Reid quotes 

 merely uses a little more force in making essentially 

 the same remark. But he can defend himself — if he 

 cares to. 



If, then, there are " sects " among biologists, I 

 should be inclined to ask : Which of them does not 

 employ — or, rather, attempt to employ — crucial test- 

 ing? Apparently Sir Archdall Reid does not study 

 the periodicals with which I am familiar ; but possibly, 

 as a medical man, he reads Parasitology. I, too, 

 happened to look at its last number, and I observed 

 an inquiry by Mr. P. A. Buxton into the specific dis- 

 tinctness of the mites responsible for three forms of 

 mange. A form known as Norwegian crusted scabies 

 has been the subject of divergent views, and "it is," 

 says Mr. Buxton, " much to be desired that someone 

 who is fortunate enough to see a case should infect a 

 few volunteers in order to discover whether ordinary 

 itch or the crusted variety is induced, and whether, 

 after one or two generations, the mites can in any 

 way be distinguished from typical 5. scabiei var. 

 hominis." This is an application of the crucial test; 

 but Sir Archdall Reid may retort that it is only 

 another of the lakes in an Africa of malpractice, and 

 since I cannot swamp your pages with all the other 

 lakes I must leave him to wander in the desert. 



Sir Archdall Reid offers to help me on the question 

 of recapitulation ; but I would ask him first to explain 

 his " glaring truism." He writes, " Variation is the 

 sole cause of non-inheritance, etc." Surely " varia- 

 tion " in this sense is but another name for " non- 

 inheritance," and the rest of his sentence therefore 

 merely states that the offspring resembles the parent 

 when it does not differ from it. But if there is any 

 other meaning in the sentence, then I would remind 

 him that whether " like exactly begets like when 

 parent and offspring develop under like conditions " is 

 just one of the questions that divide biologists. A 

 germinal change would be a change of the conditions, 

 and is therefore excluded. Either " the glaring 

 truism " is an Identical proposition, or it is a state- 

 ment actually disputed. In neither case Is It the same 

 as the statement that, " apart from variations, off- 

 spring tend to recapitulate the development of their 

 parents." If Sir Archdall Reid thinks that It really 

 Is the same, he Is scarcelv the man to dispel our 



NO. 2703, VOL. 107] 



difficulties. Those difficulties are not implicit In 

 either of his "truisms." F. A. Bather. 



August 14. 



The Fauna of Scottish Lochs. 



In Mr. B. B. Woodward's interesting letter on the 

 occurrence of Pisidium Clessini in Loch Ness (Nature, 

 August 4, p. 715) he does not mention the depth at 

 which his specimens were found. Loch Ness, in the 

 deeper parts of which Pisidium has been dredged on 

 more than one occasion, is a very deep lake in which 

 different zones of life undoubtedly occur. In Lake 

 Biwa, In Japan, the Palaearctlc' P. ca^erfanum is 

 found only at considerable depths (17-30 fathoms), 

 and it is probable that in Scotland P. Clessini lives 

 still deeper. 



Last month (July) I spent investigating the 

 fauna, and especially the molluscs and sponges, of 

 two comparatively shallow lakes in Perthshire, Loch 

 Lubnaig and Loch Vennachar. No evidence was 

 obtained in either lake of the occurrence of a deep- 

 water fauna or of the existence of molluscs at greater 

 depths than 70 ft., at which a Pisidium (probably not 

 P. Clessini) was fairly common ; but the area below 

 100 ft. is there very small. The only other molluscs 

 common in the two lakes were Limnaea peregra and 

 '' Ancylus fluviatilis,'^ both of which also occur in the 

 streams that flow out of them. The fades and habits 

 of the Limnaea in the two lakes are different. I hope 

 to discuss the reasons why elsewhere. 



Thirteen years ago I directed attention to our ignor- 

 ance of the fresh-water sponges of Scotland. Since 

 then nothing further has been published, though Mrs. 

 Scharff (Miss Jane Stephens) has given us an admir- 

 able account of the Irish species. In Loch Lubnaig 

 the abnormally low water of last month afforded un- 

 usual opportunities for the study of these interesting 

 organisms. Three species {Spongilla lacustris, auct., 

 S. fragilis, Leidy, and Heteromeyenia Ryderi, Potts) 

 were found, mostly in the form of small, thin films 

 on the lower surface of stones that would have been 

 almost inaccessible In ordinary circumstances. 



I may also mention another interesting observation 

 made at Loch Vennachar, namely, that a Tubificid 

 worm common at the edge of the lake has the habit 

 of encysting in the earth when the water retreats. 

 Each cyst contains from one to twelve individuals 

 closely coiled and in a state of apparent torpor. 

 When the cysts are placed In water the wall bursts 

 and the worms emerge in a lively condition. 



N. Annandale. 



Isle of L'lva, Argyllshire. 



Magnetic Double Refraction in Smokes. 



The letter from Prof. Elihu Thomson on "A Novel 

 Magneto-optical Effect " which appeared in Nature 

 of June 23, p. 520, suggested to me that the pheno- 

 mena were associated with inagnetic double refraction. 



I used a Nernst lamp with a vertical wire ; a 

 parallel beam of light, polarised through a NIcol with 

 the principal section at 45°, passed along a diameter 

 close to the superior plane of a circular plate coil dis- 

 posed horizontally ; and, finally, a second Nicol crossed 

 with the first. 



At the bottom of the coil was arranged in a con- 

 venient way an arc lamp with metallic electrodes, 

 able to give large quantities of smoke when carrying 

 30 amperes and 140 volts. A copper pipe, coaxial 

 on the top with the coil, conveyed the fumes on the 

 side of the magnetic field crossed by the polarised 

 light, and was disposed so as to prevent disturbing 

 light from the arc in the observation space. The coil 



