482 



NATURE 



[February 8, 191 - 



and with n considerable saving of time and trouble. Once 

 the |K)sition of the substage condenser is altered the whole 

 system of illumination from the substage condenser to the 

 source of light is displaced, which must again be adjusted, 

 so that we have to eflecl centring at various points on the 

 optical bench. This is entirely avoided by having the 

 substage condenser supported in a fixed sleeve, and the 

 centring screws attached to the objectives or the nose- 

 piece. 



.As regards the draw-tube, the point is that the use of 

 the mechanical draw-tube is advocated more in England 

 than are the correction collars, but vice versd on the 

 Continent. When one is using an objt-ctive without correc- 

 tion collar, which is extremely sensitive to differences in 

 thickness of cover glasses, it is not at all necessary to 

 resort to a mechanical draw-tube if one's instrument is 

 fitted with a carefully made simple draw-tube as is gener- 

 ally provided in the best Continental stands. 



it may be mentioned, however, that still better results 

 would be obtained by resorting to the use of a cover- 

 glass gauge, an instrument which is very valuable and 

 ine.vpensive, but rarely used by workers. In dealing with 

 the standardisation of the microscope, the matter of cover 

 glasses, which is a serious one, should also be considered 

 with the view of providing microscopists with covers of 

 much more uniform thickness. 



Mr. Sutcliffe, in his letter which appeared in Nature 

 of January 18, asks if there is any evidence obtainable 

 that the English instrument has lost its premier position. 

 We have not far to seek the necessary information, and 

 when the facts are known we cannot consider the English 

 instruments " degenerate," as the present models are much 

 superior to their predecessors. The best English micro- 

 scopes are a credit to any well-organised manufactory. 

 The Germans, however, have advanced further in the direc- 

 tion of providing more perfect instruments, which are 

 produced in vyorks better organised and with more highly 

 scientific arrangements. 



The instruments that combine in the highest degree 

 simplicity, efficiency, and durability are the most valuable 

 to the serious workers, and these features are strongest 

 in the best Continental microscopes. 



I do not believe any amount of discussion would bring 

 us to a decision so satisfactorily as a close examination 

 of instruments which have been in use for a number of 

 years in the principal laboratories throughout the world. 

 In fact, we need hardly look outside our own little island 

 for the result, as there is plenty of material at home to 

 deal with for a settlement of the dispute in a most practical 

 "lanner. J. W. Ogilvy. 



18 Bloomsbury Square, London, W.C, January 30. 



The Mnemic Theory of Heredity. 



In a review of the third edition of Prof. Richard Semon's 

 well-known book upon this subject, in Nature of 

 January 18 (p. 371), the reviewer writes as follows :— 



Ihe mnemic theory, which is based upon a belief in the 

 mheritance of acquired characters, naturally does not 

 appeal^ to those who deny the po.ssibility of such inherit- 

 ance." From the point of view of modern embrvological 

 research, both of these statements are open to challenge. 

 The founder of this mnemic theory, or " memory as a 

 general function of organised matter," has indeed written 

 very little upon the subject, which he first broached in a 

 public lecture in 1870. At the date named, when Prof. 

 Ewald Hering, now of the University of Leipzig, gave his 

 classic address, I imagine that the question of the inherit- 

 ance or non-inheritance of acquired characters had hardly 

 been raised. By a curious coincidence, it was in the same 

 year that Prof. W. Waldeyer in his researches set up the 

 doctrine of the somatic origin of germ-cells from the 

 " gerniinal epithelium," and obviously this doctrine of the 

 somatic or bodily origin of germ-cells is demanded bv the 

 view of an inheritance of acquired characters. The history 

 of embrvological research upon the germ-cells during the 

 present century demonstrates clearlv that in his researches 

 in the lower vertebrates the writer first established— in 

 1900— an actual tangible continuity of germ-cells from 

 generation to generation, and the absence of any genetic 

 NO. 2206, VOL. 88] 



connection between Waldeyer's " germinal epithelium ' 

 and the germ-cells, that in many other caset these find 

 have been, and are still being, confirmed by the inv< 

 tions of other observers, and that Prof. Waldeyer ii 



some years ago withdrew his former researches in f.^ 



of such a continuity of germ-ceils as underlying the life 

 cycle. Indeed, he wrote : — " The consequences of thi 

 doctrine of the continuity of germ-cells are almost in 

 calculable for every branch of biology " ; so that now fa 

 animals a fundamental postulate of the doctrine of ai 

 inheritance of acquired characters has vanished. 



But, as a fact, the inheritance of acquired charact*--- ■ 

 more a botanical doctrine than a zoological one. In 1 

 this apparent inheritance of such characters is confio' 

 the asexual generations, in which, if the term " individual ' 

 be used, it must apply to all the products, asexually pro 

 duccd, of one original plant — that is, in this sense thej 

 would all form a single individual. As an instance, ir 

 this way all the countless plants of the white chrysanthe 

 mum, Niveus, would form ft single individual. Th< 

 doctrine of an inheritance of ^ai-a^ired characters d(K*s not 

 and cannot, apply to the sexual generations of animals 

 Moreover, here it is refuted by the positive finds o 

 embryology, which demonstrate, under an actual conti 

 of gt-rm-cells from generation to generation, that m 

 at all is handed on from parent to offspring. As tl 

 the case, nothing acquired by the parent can be inh- 

 That is, there is in the sexual generations of anim.i 

 such thing as an inheritance of acquired characters. 



I do not now remember when I first came to kno. 

 Prof. Hering 's theory of heredity as based in the un 

 conscious memories of germ-cells, but it must be a lonf 

 time ago. .As Samuel Butler remarks of Charles Dr. ' 

 and the doctrine of natural selection, it must have b' 

 an "unconscious memory" to me, for in my rese.T:. .. 

 into the history of the germ-cells I evolved it anew. A) 

 showing this, and as affording a simple statement of thf 

 main lines of the theory, I may quote the follow 

 written by me in 1904: — " From its nature it (the tl 

 of heredity advocated by me) might be termed ' the I 

 study -Theory of Heredity.' Given in a certain life-h; 

 the period of formation of the primary germ-cells, i ; 

 these let there be, for simplicity, but two, .AB and H.A 

 On one of these falls the lot of developing into an embr\o 

 to which of the two this happens is not of consequent 

 the argument. In all its essential characters the rem;; 

 primary germ-cell (whose immediate destiny it is to b< 

 the founder of the ' sexual products ' of the said eni 

 is the exact counterpart of the developing one. So ; 

 so is this the case that, if both form embryos, the*' 

 identical twins. In the ancestry neither of the pri: 

 germ-cells, .AB and B.A, had ever been a higher animal 

 neither they nor their ancestors had ever formed part o 

 the body of a higher animal. But their ancestry is con 

 tinuous with a long line of germ-cells, and at reguiai 

 intervals these were exactly like certain sister-cells, whici 

 did develop and form higher animal individuals. .Althougf 

 the cell .AB does not itself give rise to an embryo, in th« 

 meantime it retains for itself, and also for all its immediati 

 progeny, the properties of B.A, those characters or poten 

 tialities which, were it or any of its progeny to develop 

 would make it or them identical twins with B.A, the othei 

 cell which did develop. This is the greatest wonder it 

 embryology! In the drama of heredity there are alwayj 

 understudies, which for a certain essential period an 

 endowed with all the identical properties (potentialities) ot 

 that germ-cell from which the player arises. These under 

 studies, the primary germ-cells, are never employed upor 

 the stage as such — except in the instances of identica 

 twins, triplets, &c. — but some of them in new guises anc 

 after new conjugations or unions are the immediatt 

 ancestors of those which become the acting characters ir 

 new scenes of the cjxlical drama of Life." 



The original German of Prof. Hering 's lecture, like 

 .Austrian German in general, is difficult, and probably thf 

 original is little known in this country, although an excel- 

 lent translation was published in Butler's " Unconscious 



J B«ird, J., " A Morpho!osical Contmuity of Germ-CelU as the Bas's o 

 Heredity and Variation, ' in Revitvi of Nettrology and Psyehiai'\. vol. ii 

 1904, P- 141- 



