February 8, 19 12] 



NATURE 



48. 



Memory " (1880, new edition 1910). To me, as an advo- 

 cate of this theory of heredity, it comes as something 

 new — and strange — that underlying it there should be the 

 assumption of an inheritance of acquired characters. I 

 would rather conclude that, like Francis Galton, this 

 illustrious physiologist — with the " prevision " of which 

 Pasteur so often spoke — foresaw that the individual was 

 not at all " a chip of the old block," but that at the basis 

 of all development there was a continuity of germ-cells. 

 For on p. 17 of Ostwald's reprint of the original lecture 

 Prof. Hering writes : — " From this point of view the whole 

 individual development of a higher organised animal forms 

 a continuous chain of memories of the development of that 

 great series of beings whose final link this animal 

 represents." 



Like the late Samuel Butler, the writer rediscovered 

 this theory of heredity, and except that author he was the 

 first to advocate it, upon grounds of observation, in this 

 country. As undoubtedly it is of all theories of heredity 

 ihe theory which is capable of accounting for and explain- 

 ing all the facts, I venture to ask the courtesy of the 

 insertion of this brief account of it in your pages. In the 

 light of this overwhelmingly important theory the 

 " Mendelian discovery," for example, sinks into its proper 

 place as a small but interesting episode in the history of 

 h' rcdity. J. Beard. 



s Barnton Terrace, Edinburgh, January 22. 



between each two successive sexual generations, and the 

 latter develop each from a single non-sexual cell, the spore, 

 produced by the sporophyte generation after it has attained 

 maturity. Here, at any rate, there is no continuous chain 

 of germ-cells distinguishable from somatic cells. 



Dr. Beard's views on the subject of identical twins are 

 new to me. I was under the impression that such twins 

 were supposed to result from the complete division of a 

 single fertilised ovum. This, at any rate, is the view 

 adopted by Weismann. Arthur Dexdy. 



1 AM unable to agree with Dr. Beard that the mnemic 

 theory of heredity does not involve acceptance of the 

 1 doctrine of the inheritance of acquired characters, 

 j, Certainly the theory as enunciated by Prof. Semon, which 

 I formed the subject-matter of my review, is based upon 

 such acceptance, to justify which weighty evidence is 

 brought forward. Can an organism, or a germ-cell, be 

 said to remember events of which it has had no past 

 experience, direct or indirect? If, as Dr. Beard holds, 

 neither the primary germ-cells nor their ancestors have 

 ever formed part of the body of a higher animal, can they 

 be supposed to remember events in the ancestral history 

 of the race, unless, of course, they have received informa- 

 tion as to such events (engrams) from the bodies in which 

 they are, or were, enclosed? The power of transmitting 

 such engrams to the germ-cells is the fundamental con- 

 ception of the doctrine of the inheritance of acquired 

 characters, as it is also of the mnemic theory as ex- 

 pounded by Prof. Semon. If, however, Dr. Beard holds 

 that the germ-plasm does not receive engrams from the 

 body at all, but is merely a continuous stream of living 

 matter which has the power of producing some particular 

 type of body at intervals and under appropriate conditions, 

 I fail to see where the idea of memory comes in, any more 

 than in the case of the periodic waves produced bv the 

 tide. 



I cannot see that the doctrine of the somatic or bodily 

 origin of the germ-cells has any necessary connection with 

 the doctrine of the inheritance of acquired characters. 

 Even if we adopt the opposite doctrine, that the germ-cells 

 form a continuous chain from generation to generation and 

 are separated from the somatic cells at the very commence- 

 ment of individual development, such a view does not 

 jseriously affect the question, for there is no valid reason 

 lor supposing that the germ-cells could be influenced by the 

 somatic cells only through some protoplasmic connection. 



Again, why should any distinction be drawn between 

 plants and animals with regard to the problem under dis- 

 cussion? It would indeed be strange if the two great 

 divisions of the organic world should differ in this respect. 

 Of course, in the higher plants, the sexual generation 

 (gametophyte) is very greatly reduced, but none the less 

 a true sexual process intervenes between each asexual 

 (sporophyte) generation and the production of the ripe seed. 

 The case of the peach trees quoted in my review is in no 

 way comparable to Dr. Beard's chrysanthemums, for the 

 smbryo plant within the seed is deveJoped from a fertilised 

 egg as truly as in the case of any animal. It is obvious, 

 moreover, that in the case of the higher plants Dr. Beard's 

 view as to the relations of the germ-cells cannot be main- 

 tained, for the whole sporophyte generation intervenes 



The " Isothermal Layer." 



I AM inclined to doubt whether Commander Hepworth's 

 suggestion (Nature, January 25) that the so-called " iso- 

 thermal layer" is simply due to radiation from the 

 material, solid or gaseous, which circulates round the sun 

 with an orbital motion and gives rise to the zodiacal light, 

 can be reconciled with the configuration of the surfaces of 

 equal temperature in the upper air which show a pro- 

 gressive increase of temperature from low to high latitudes. 

 It seems more probable that this increase, and the fact that 

 above a certain height in these latitudes the temperature 

 no longer diminishes with the altitude, are the result of 

 the prevalent movement, outside the equatorial belt, of 

 the higher portion of the atmosphere from west to east 

 with comparatively great velocity, which increases with the 

 latitude and altitude, and extends to lower levels as the 

 distance from the equator becomes greater. This move- 

 ment, which gives the upper atmosphere greater angular 

 velocity than the lower and the earth beneath, partiallv 

 counteracts the force of gravity and causes the air to rise 

 and expand without doing work, and therefore without 

 suffering a decrease in temperature. At the equator there 

 appears to be no satisfactory evidence of an " isothermal 

 layer." 



But although the radiation from the orbital inter- 

 planetary matter of the zodiacal light may not afford an 

 explanation of the " isothermal layer," it must be taken 

 into account as a climatic factor. Maurer has shown that 

 the earth receives at night radiated heat to the extent 

 of 037 of a calorie per square centimetre per minute. 

 This is attributed — no doubt in the main correctly — to 

 radiation from the carbonic acid and water vapour of the 

 atmosphere, but some portion must have an external 

 source. It is possible that the radiation from inter- 

 planetary material may at present be almost as inconsider- 

 able as that from the planets or the fixed stars ; but if. as 

 we have every reason to believe, there has been a gradual 

 approximation of this diffused orbital matter towards, and 

 absorption in, the sun, there must have been a time when 

 so much was present beyond the earth's orbit that the 

 radiation received from it balanced to a considerable extent 

 the radiation from the earth into space, and rendered not 

 only the daily and seasonal variations of temperature, but 

 also the permanent differences of temperature between 

 high and low latitudes, much less marked than they are 

 at present. 



I have for some time thought that it was in this direc- 

 tion we ought to look for the explanation of the com- 

 parative uniformity of temperature that appears to have 

 prevailed in different latitudes in Pala'ozoic times, a 

 uniformity that seems to have existed as much in periods 

 of cold as of high temperature, and the absence of marked 

 seasons even in the far north, evidenced by the fact that 

 the remains of stems with exogenous growth show little 

 or no trace of annual rings. In the long Arctic night, not 

 only heat, but light, would have been continuously re- 

 ceived from this source. How considerable, even nt pre- 

 sent, is the illumination given by the zodiacal light can 

 only be realised by those who have travelled in mo<jnless 

 nights in the tropics. Even in forest country with a cloudy 

 sky the darkness of midnight is changed about 2 a.m. to 

 a twilight, which is quite sufllcient to render the track 

 visible until the true dawn appears. 



Xordenskiold has given reasons for believing that tinp 

 cosmic dust revolves round the earth itself as centre. If 

 this be the case, its climatic influence in the past may 

 have been similar, but it was probably of much less 

 importance. Jous VV. Evans. 



'January 27. 



NO. 2206, VOL. 88] 



