214 



NA TURE 



[August i 2, 1922 



development of the male sexual elements in Crepidula 

 is certainly independent of season, and so also 

 apparently is that of the female sexual elements, 

 since Crepidula breeds almost continuously from 

 about March to December. 



The males of Crepidula can certainly recognise 

 females by some particular sense as yet unknown, 

 as will be seen from the following facts. In examin- 

 ing a large number of chains of Crepidula (see Orton, 

 1909, loc. cii.), small to medium Crepidula were often 

 found isolated and settled on the left-hand side of 

 the females. Now this is the wrong side to permit 

 of copulation, but in spite of the fact that copulation 

 could not be effected these individuals were found 

 to have an unusually fat and extensible penis capable 

 of stretching probably twice as far as usual. In the 

 experimental observations described above it was 

 found that isolated Crepidula — certainly not older 

 than those settled in the wrong place — had their 

 penis absorbed. The conclusion is obviously reached 

 that the males on the females knew that the latter 

 were there and tried their best to reach them, whilst 

 the totally isolated ones have resigned themselves 

 unreservedly to a complete sex-change. It is only 

 since proof has been obtained of rapid sex-change 

 following complete isolation that a satisfactory 

 explanation could be given for the phenomena of 

 the misplaced males, but the explanation given 

 above has for a long 'time been suspected of being 

 the correct one. J. H. Orton. 



Marine Biological Laboratory, The Hoe, 

 Plymouth, July 25. 



Wegener's Displacement Theory. 



I quite agree with Mr. Lake's remarks (July 15, 

 p. 77) as to the unsuitability of the tracing-paper 

 method of investigating the merits of Wegener's 

 hypothesis. All who wish to pursue the subject will 

 do well to adopt his suggestions as to the practical 

 method. 



For some time I have been engaged on the subject, 

 and, though I must plead guilty to the use of the 

 tracing-paper method in the first instance — and 

 there is this to be said in its defence, that we are 

 attacking the master with his own weapon — results 

 certainly warrant Mr. Lake's mild censure that for 

 the truth of Wegener's theory to be accepted we 

 must also believe in a great degree of plasticity for 

 the earth's crust. 



If the American coast be superimposed on that of 

 Africa, the parts that coincide (according to Wegener, 

 with a divergence of never more than 100 kilometres) 

 are confined to that represented on the African coast 

 by the distance from Kamerun to a point slightly 

 north of the mouth of the Orange River. There is a 

 divergence along the coast of Cape Colony, and an 

 angle of approximately 15° between the superimposed 

 coast of South America (N.E. coast of Brazil, etc.) 

 and the African coast along the Gold Coast, Ivory 

 Coast, Liberia, etc. These divergences may be 

 easily accounted for by comparatively recent denuda- 

 tion, or fracture. 



Assuming the truth of fracture — after Wegener — 

 along the line Kamerun to Orange River, the Zwarte 

 Bergen of Cape Colony certainly do fall into place 

 exactly with the Permian cordillera of the Pampas. 

 But this added coincidence merely leads us into 

 greater difficulty. For to make the superimposed 

 American coast coincide with the African coast in 

 this manner, we have to swing the American continent 

 through an angle of 45 ° from its present position; 



This leaves us with Newfoundland in the position 

 approximately 45 W., 32 N. — in the Atlantic Ocean. 



NO. 2754, VOL. I io] 



The Hercynian Appalachians — another of Wegener's 

 "test" ranges — appear in a position in the 

 Atlantic north of Cayenne, stretching in a general 

 N.N.E. direction (along the fine 52 W., S N. — 47 W.. 

 20 N.). They are in the right direction for joining 

 up with the British Hercynian range, but are separated 

 therefrom by a distance of ocean above 2000 miles. 



To lessen this distance, and bring it within a 

 reasonable distance of the British Hercynian range 

 for joining-up purposes, we cannot allow any bending 

 of the American continent. Any alteration in the 

 relative positions of North and South America 

 throws the direction of the Appalachians out 

 absolutely and entirely. The only way the joining-up 

 can be done for both the Zwarte Bergen-Buenos 

 Ayres range and the Hercynian range on both sides 

 of the Atlantic is either (1) a great movement of 

 the Eurasian continent south-west, or (2) a movement 

 of the African continent south to a distance of about 

 500 miles from its present position, and at the same 

 time a rotation about an axis somewhere in the 

 neighbourhood of Suez (for example) of not less 

 than 50 . 



In other words, since the fracture, either the 

 Eurasian continent has been rotated in a general 

 S.E. direction (clockwise) or the African and Indian 

 masses in a N.E. direction (counter-clockwise), or both 

 these motions have taken place, from a centre 

 somewhere in the Suez-Madeira Islands line. 



Are the Himalayas, the Carpathians, the Alpine 

 system, the Atlas Mountains, the result of the 

 clashing together of the African-Indian, European- 

 Asiatic continents by these movements ? As Prof. 

 Sollas has reminded me, the first word on Wegener's 

 theory lies with the astronomers and physicists. 

 To them I leave the task of finding a force which 

 has acted in two parallel directions west on the 

 North and South American continents, making their 

 advance west without rotation relative to each other 

 and overcoming the resistance at the expense of the 

 Andes Cordillera and its continuation in North 

 America, and has at the same time driven the Eurasian 

 and Asiatic continents south-east and the African- 

 Indian continent north-east (relative to the Americas) 

 with such determination that the great folding of 

 the Himalayas-Alps line resulted — and waited until 

 Tertiary times to do most of it. 



E. R. Roe-Thompson. 



St. Edward's, Oxford. 



The Elliptic Logarithmic Spiral. 



I am much obliged to Mr. Wright for his_ correction 

 (Nature, July 8, p. 40). I had made a search in 

 English and Continental books on curves and con- 

 cluded that this spiral had been overlooked as a 

 curve. But it appears to have been recognised in 

 connexion with the spherical pendulum. Prof. Lamb 

 in bis " D3 r namics, " p. 2S8, as I now find, refers to 

 the curve as "a kind of elliptic spiral," and Dr. 

 Besant describes it as " an ellipse gradually shrinking 

 in size." 



I take, however, a little unction in having given 

 the curve a name, especially as it seems to be of 

 importance in damped elastic systems with one 

 degree of freedom, and in fact it may be called a 

 characteristic. Thus in the elastic system without 

 friction, the force displacement diagram is a straight 

 line; with fluid friction varying as the velocity, we 

 have the elliptic logarithmic spiral; and with solid 

 friction, a series of parallelograms. The dissipation 

 per cycle, its rate during the cycle, as well as what 

 may be termed the timbre of the motion, are in this 

 view brought out very clearly. H. S. Rowell. 



15 Bolton Road, W.4. 



