EVOLUTION 959 



lengthened and broadened, bent or even twisted, into protean 

 changes of features and expression. Our author, however, does the 

 like throughout wide ranges of form, and with serious, and serial, 

 thoroughness, by drawing a simple form on a regular network of 

 co-ordinates, and then variously modifying these: at first in the 

 simplest possible way, by vertical lengthening or horizontal broaden- 

 ing, and then with further changes mathematically suggested, 

 followed, and explained. Even in the first of such modified graphics 

 the widely different dimensions presented by homologous parts — 

 say the increasingly slender metacarpals and digits of ox, sheep, 

 and giraffe^ — are well shown as a continuous series. He reproduces 

 drawings of heads made by Diirer upon his own networks of co- 

 ordinates, modified in different proportions, or even tilted obliquely, 

 with changes of facial angle, features, and expression accordingly. 

 Next he applies the like principle and method to express the widely 

 contrasted aspects of allied genera of many kinds, from among 

 crustaceans, or hydroids, to series of allied fishes, so that the most 

 eccentric and deformed-looking tj^es are graphically shown as but 

 modifications of simpler forms. Different types of reptilian and 

 avian pelvis are thus arranged in well-gradated growth-series — a 

 matter of no small evolutionary interest. With continued develop- 

 ment of his graphic projections, what are to ordinary sight widely 

 different forms of mammalian skulls are brought to amazing simi- 

 larity; and so at length for the comparison of the human skull with 

 that of animals. The great point thus is that leaf, pelvis, or skull, 

 crustacean, fish, or human face, are each varying as a whole, or at 

 any rate are thus clearly conceivable. 



Recall now the classical interpretation of organic variations, 

 usually small and seeming spontaneous and indefinite, as for in- 

 stance so clearly expressed by Wallace, with his and Darwin's 

 explanation of structural details in terms of their assumed separate 

 origins, as in a flower for convenient example; and next the con- 

 trasted general growth-interpretation of floral forms such as have been 

 illustrated above. In Thompson's work, however, this general growth- 

 interpretation of changes in details is at length more fuUy investi- 

 gated and presented, and generally applied. The argument thus 

 speaks for itself: but it obviously invites the comment that it is 

 fuU time for the treatment, by Darwinians and neo-Darwinians 

 alike, of the whole question of variations, in their long customary 

 terms, to be fundamentally revised. 



Thompson's treatment of growth-processes, as widely transforma- 

 tive, may also here with advantage be correlated with Child's 

 suggestive investigation of metabolic gradients, since these may 

 surely be brought into close and even complemental relation. 



Neither of these theories seems as yet to take account of that 

 rhythmic contrast, yet co-adjustment, of the processes of growth 



