August 1, 1890.] 



KNOWLEDGE 



197 



this cell-clustering would be that the cells fell into two 

 classes, body-cells and germ-cells. While the former were 

 concerned solely with the nutrition of the organism, losing 

 in this specialisation of function the power of reproduction, 

 that function became concentrated in the germ-cells, or, 

 speaking more jirecisely, in the germ-plasm, " the un- 

 dying part of the organism,'' which is located in the 

 nucleus of the germ-eel!. It is these germ-cells which 

 Professor Weismann contends are the immortal part of the 

 Metozoa. "It is necessary," he says, "to dis'.inguish 

 between the mortal and the immortal part of tlie individual 

 — the body in its narrow sense (the soma, as Prol'cssor 

 Weismann, applying the Greek word for body, calls it) and 

 the germ-cells. Death affects only the former ; the germ- 

 cells are potentially immortal, in so far as they are able, 

 under favourable circumstances, to develop into a new 

 individual, or, in other words, to surround themselves with 

 a new body (wi »»«)."•' With increasing sub-division of 

 function, there has been increasing modification of the 

 organism, increasing complexity of parts, but the twofold 

 classification of the cells has remained. The death of the 

 body-cells is involved in the ultimate failure to repair 

 waste, because a worn-out tissue cannot for ever renew 

 itself, and because cell-division has its limits. Death also 

 becomes a necessity, being of advantage to the species, the 

 needs of which likewise determine the duration of the 

 individual life. 



Now as it is impossible for the germ-cell to be, as it 

 were, an extract of the whole body, and for all the cells of 

 the body to despatch small particles to the germ-cells from 

 which these derive their power of heredity — the funda- 

 mental idea, it will be remembered, in Darwin's provisional 

 theory of Pangenesis, namely, that all the cells throw 

 off gemmules, which ultimately become concentrated in the 

 reproductive elements — the germ-cells, so far as their 

 essential and characteristic substance is concerned, are not 

 derived from the body of the individual, but directly from 

 the parent germ-cell. Heredity, then, according to 

 Professor Weismann, is secured by the transference from one 

 generation to another of a substance with a definite 

 chemical and, above all, molecular constitution, and he 

 names this theory " The Continuity of the Germ-Plasm." 

 This germ-plasm is assumed to possess a higlily complex 

 but extremely stable structure, conferring upon it the 

 power of developing into a complex organism. So stable is it, 

 that " it absorbs nouri.shment and grows enormously with- 

 out the least change in its complex molecular structure."! 

 Of this germ -plasm it is assumed (we find no lack of 

 assum])tion) that a small portion contained in the parent 

 egg-shell is not used up in the construction of the body of 

 the offspring, but is reserved unchanged for the formation 

 of the germ-cells of the following generations. " One 

 might represent the germ-plasm by the iiii'taphor of a long 

 creeping root-stock from which plants arise at intervals, 

 these latter representing the individuals of successive 

 generations."! 



Only variations of the germ-plasm itself are inherited, 

 and it is upon these variations that natural selection 

 operates, (lie it always remembered that, in Darwin's 

 own words, " unless profitable variations occur, natural 

 selection can do nothing.") Variations are due. Professor 

 Weisnuinii says, to the process of reproduction by which 

 the larger number of existing organisms are propagated. 

 This process combines two groups of hereditary tendencies 

 derived from the mingled germ-plasms of the male and 



* JCmiii/s, p. 122. 

 t Jl'id., p. 271. 

 I IOkI. , j). L'OG. 



female parents, resulting in those individual difl'erences 

 which form the material from which new species are pro- 

 duced by the action of natural selection. Those differ- 

 ences multiply in geometrical ratio, so that " in the tenth 

 generation a single germ contains 1,024 dift'erent germ- 

 plasms with their inherent hereditary tendencies, and, as 

 continued sexual reproduction can never lead to the re- 

 appearance of exactly the same combinations, new ones 

 must always arise. "•■■ Sexual reproduction coidd alone 

 " have called into existence that multiplicity of form of tlic 

 higher animals and plants, and that constantly fluctuating 

 union of individual variations, of which natural selection 

 stood in need for the creation of new species."' 



Such, in as brief outline as lies in our power to make, is 

 the remarkable theory which ij causing no light searchings 

 of heart among the Bereans of Evolution, and renewed 

 study of their scriptures to see whether these things are 

 so. The most staggering blow which Professor Weismann 

 has dealt against current beliefs is in the denial of the 

 transmission of individually-acquired characters which is 

 involved in his assumption of the continuity of the germ- 

 jilasm. Certainly, if in this matter he has not proved bis 

 case, he has exposed the insufficiency of the existing 

 evidence against it. For what he says is that the 

 structure of the offspring depends on the germ-plasm, and 

 as this has no break in its continuity, but remains un- 

 att'ected by any changes occurring within the body cells, 

 the structure remains identical. It matters not what may 

 be the action of external influences, or of the use or disuse 

 of certain organs ; any changes induced thereby in the 

 parent are not transmitted to the oti'sprmg. The parent 

 is only the medium by which the germ-plasm repeats in 

 the offspring the physical and mental structure of tlie 

 ancestors, so that, as Grant Allen aptly puts it in his review 

 of Professor Weismann's Essays, J " parent and offspring 

 resemble one another, not because the parent produces 

 the offspring, but because both arise from the self-same 

 substance, which merely develops earlier in the parent and 

 later in the offspring. To use a transparent metaphor, the 

 father is thus reduced to the position of an elder brother 

 to his own son." Professor Weismann restricts the term 

 " acquired characters" to those features which make their 

 first appearance in the individual, and which are due to 

 mode of life different from tliat of its ancestors, to change 

 of climate, variety of food, and to other agencies. To these 

 may be added effects of mutilation. All such he classes 

 as " somatogenic," because they follow f'rciin the reaction 

 of the soma under external intlueiu-es. It is these which 

 he contends are not transmitted. 



All other characters are classed as '• blastogenic," 

 because " they include all those characters in the body 

 which have arisen from changes in the germ, and all the 

 changes produced by natural selection operating upon 

 variations in the germ."§ 



So the sum of the matter is, that natural selection is all 

 in all, and that use and disuse, and action of the envu'on- 

 ment, count for nothing, or, perhaps, a very little, for upon 

 this we have " two voices ' in the Hxxiiiik. The induence 

 of the agents to which, as Darwin grew older and widened 

 his range of observation, he was disposed to give greater 

 weight, and the large place of which in the production of 

 specific characters is maintained by Herbert Spencer in his 

 Factoix <;/' (hyaiiir KroliitiiDi, is denied by Professor 

 Weismann. 



Our remaining space must be given to a few of the 



» Ess,n/s, p 276. 



t Professor Weismann. in Xatnre. I! Fell. 18;iO. p. :i22. 



J Aruikmy, 1 Feb. Itj'.IO. 



I'Kssiiijs, p. 413, 



