266 



NATURE 



[January 17, 1895 



tial but integral, not qualitative but quantitative, and 

 this undermines the most important of Weismann's 

 positions. 



Very important are Dr. Hertwig's criticisms on the 

 doctrine of determinants, so sharply and clearly defined 

 by Weismann. This doctrine is inseparably connected 

 with that of the anisocleronomic division of the germ- 

 plasm, and it might appear that if the l.itter is disproved, 

 it is unnecessary to enter into a detailed criticism of 

 what depends upon it. But the criticism is not without 

 its utility, since. Dr. Hertwig shows us, the conception 

 of determinants is only an extreme instance of a false 

 conception of causality common in current biological 

 literature. Weismann has supposed that the ultimate 

 vital particles, which he calls biophors, are grouped in 

 the germ-plasm into " determinants," and that every 

 smallest cell-group in the adult organism which has 

 definite characteristics and a definite situation is repre- 

 sented in the germ-plasm, both of ovum and sperma- 

 tozoon, by a definite determinant. These last are so 

 arranged in the germ-plasm, and are endowed with such 

 special forces, that they are able, in the course of 

 ontogeny, to move at the right time into the right place— 

 this movement being effected by the almost purposive 

 anisocleronomic division of the germ-plasm. This very 

 definite idea is founded on an erroneous conception of 

 the relations between primordium (Anlage) and prim- 

 ordial product, which are supposed to stand in rela- 

 tion to one another as cause and effect. More or 

 less unconsciously, the biologist commonly assumes 

 that, because a given animal proceeds of ne-essity 

 from a given egg, there is an identity between 

 primordium and primordial product ; so much so, that 

 the developing organism is often spoken of as if it were 

 a self-contained system of forces, a sort of organic perpe- 

 tuum mobile. He overlooks the fact that for the fulfil- 

 ment of the developmental processes many other condi- 

 tions are necessary, without which the primordium could 

 never arrive at the condition of its final product. Between 

 the two there is clearly no identity, and it is false and 

 mischievous to suppose, as the older evolutionists did, 

 and the new evolutionists are again trying to make us 

 believe, that the perceptible heterogeneity of the last 

 stage of the developmental process is only the final ex- 

 pression of an invisible corresponding heterogeneity of 

 the first stage. Throughout the whole of the ontogeny 

 there is an exchange of material taking place, the adult 

 has arrived not only to its bulk, but to its complexity as 

 the result of metabolism ; inorganic material is perpetu- 

 ally changed into organic, and serves for the growth and 

 development of the primordia. It is true that the form 

 changes are constant and invariable for the species, from 

 a certain kind of germ a certain kind of animal is invari- 

 ably produced ; but is not this largely because, in the 

 ordinary course of events, the oviceil is always subject 

 to similar conditions of assimilation and excretion, and to 

 similar conditions of gravity, light, temperature, &c. .' 

 Throughout the course of organic develupiiient things 

 which were external are transformed into things internal, 

 and the primordium grows and ii changed at the expense 

 of the environment. In thus recalling to our attention the 

 fact that an organism is above all things metabolic, 

 that its growth and changes are the result of its metabolic 

 NO. I316, VOL. 51] 



activity, and that its ultimate mass is the result of 



assimilation, of the taking up and making an integral 

 part of itself of matter which was previously apart and 

 different from itself, Dr. Hertwig does a real service to 

 biology. He forces us back to the consideration that 

 physiology and morphology are not two separate and 

 independent lines of study, but that they are so closely 

 interdependent that no generalisations can be made on 

 the evidence of one kind of observation alone : they must 

 be supported by equally cogent argu ments from the other 

 side. The theories of the evolutionists are essentially 

 morphological, and in this they resemble the theories 

 of the last century, that they take no account of one 

 of the most wonderful of all vital phenomena, that 

 of metabolism, but strive to find an explanation of the 

 ultimate perceptible differences in form by asserting 

 that the differences were always there, and have only 

 expanded so as to become perceptible. Weism.inn's 

 attempt to deal with this question by assigning the 

 power of change as the result of metabolism to the 

 biophors, does not really offer more than a purely 

 formal explanation of the question, for what he pre- 

 dicates of the biophors may very well be predicated of 

 the whole cell. Our ideas of increase of complexity 

 as the result of metabolism are made none the clearer 

 by shifting the responsibility of the change, if one may 

 express oneself so, to subordinate parts. 



It is indeed apparent, on rellection, that the characters 

 of the perfected organism are not and cannot be the 

 characters of a single cell — or even of a cell fusion such 

 as the oosperm— and the converse of this is true that the 

 characters of a cell cannot be the characters of the per- 

 fected organism. For what is a perfected metazoon or 

 metaphyte but an aggregation of cells of most numerous 

 and unlike characters.^ The characteristics of the per- 

 fected organism are the result of the correlation of 

 all its parts, of the relations of cell to cell and of 

 groups of cells to groups of cells ; and .ire we to 

 attribute to a single cell which has no relations charac- 

 ters which are essentially the results of the relations 

 of innumerable cells one to another .' 01 the importance 

 of the correlation of the parts of the perfected organism 

 we can have no doubt, nor can we escape from the 

 corollary that the ch.iracteristics of the organism reside 

 not so much in the cells themselves as in the aggregation 

 and interdependence of the cells, and if we may demur to 

 the suggestion of the colonial character of the metazoa 

 which is contained in the sentence, we must at least 

 admit much of the truth of Hertwig's statement (p. 85) : 



" That the ovum is an organism which multiplies itself 

 by division into many organisms similar to iisell, and that 

 it is through the reciprocal action (WechseUvirkung) of 

 all these m.iny elementary organisms at each stage of the 

 development that the organism as a whole is gradually 

 and progre^sively established." 



Dr. Hertwig institutes the comparison which was made 

 long ago by Herbert Spencer, between an organism and 

 a human society, and it is worth while mentioning his 

 illustration as showing his conception of the relations of 

 the cell to the organism. The organisation of a complex 

 human society, he says, is something new, and not to be 

 thought of as existing beforehand in the organisation 

 of an individual man. It is nevertheless founded in 



