372 NATURAL SCIENCE. May, 



and because if it is not true we can get no further with the problem. 

 According to Lamarck's solution of the problem of species, organisms 

 make an appropriate structural and physiological response to the 

 environment, and by the inheritance and accumulation of these, 

 species arise. According to Darwin, in the struggle for existence, 

 those of occurring variations which are in the direction of adaptation 

 survive, the others do not. Cases of adaptation, as Lamarck under- 

 stood it, are, says Mr. Bateson, significantly few, while Natural 

 Selection is a true cause. 



On the other hand, upon both theories specific diversity of 

 form is dependent on diversity of environment, and apparently 

 identical species live in most different environments, while apparently 

 closely -allied but distinct species live under apparently identical 

 conditions. In this Mr. Bateson sees an ultimate difficulty, insoluble 

 by previously-existing facts and methods. His new method is to 

 study variation. Mr. Bateson then dismisses the Recapitulation 

 Theory as corroborating only the general theory of descent, and 

 as inapplicable to the history of individual cases. He dismisses 

 also the study of adaptation until such time as there be with 

 it exact information about the actual amount of preservation caused 

 by particular adaptations. He lays great stress on the familiar diffi- 

 culty of accounting by Natural Selection for the incipient stages of 

 adaptation, and finally suggests that a study of variation may reveal 

 that the discontinuity of species arises from a discontinuity of varia- 

 tion. As he regards discontinuity in species as the chief difficulty, he 

 proposes for the present to consider evidence only of discontinuity in 

 variation. Next, Mr. Bateson proposes to consider chiefly variation 

 with regard to symmetry. In almost every living thing pattern and sym- 

 metry are a striking feature, so much so that, if we understood pattern 

 and symmetry, we should not be far from understanding organism. 

 A great part of symmetry depends on repetition of parts, and for this 

 Mr. Bateson employs the new term merism. Numerical and geometrical 

 variation is of frequent occurrence. Mr. Bateson calls it meristic, and 

 the evidence in this book deals almost entirely with it. It is of im- 

 portance, first because differences in number and symmetry are fre- 

 quently specific differences between organisms, and, therefore, because 

 meristic change has occurred in evolution. It is found that meristic 

 variation is very often discontinuous, in some cases of repetition always 

 so. This, of course, suggests that the magnitude of the integral steps 

 by which variation proceeds is often greater than most have supposed. 

 Siibstaniive variation, or variation in the actual quality of the elements 

 of an organic structure, is in most cases to be distinguished carefully 

 from meristic variation, although the two may occur in conjunction. 



He sees in merism a general law of the organic world, and there- 

 fore dismisses all attempts to make metameric repetition an indication 

 of community of descent— as, for instance, in seeking segmented 

 invertebrates as the necessary ancestors of segmented vertebrates. 

 Still more he repudiates the attempt to assign individual values to the 

 members of a meristic series, as, for instance, the attempt to definitely 

 compare and homologise the nerves in all the groups of vertebrates. 



He draws an analogy between asexual reproduction and the 

 production of a meristic series, and suggests that variation among 

 the members of a meristic series may occur just as variation, although 

 comparatively rarely, may occur among asexually-produced indi- 

 viduals. Similarly, he compares the relations between a paired 

 metameric series to the relations between the first two segmentation 

 spheres of an ovum, separation of which, as Driesch and E. B. Wilson. 



