THE METHOD OF CEEATION OF ORGANIC FORMS. 201 



2. Local increase of Growth-Force. — Examples of a local in- 

 crease of this kind are probably to be seen in convoluted organs ; 

 as the convolutions of the brain in higher Mammalia ; the convo- 

 lutions of the tooth-dentine of the Labyi'inthodont Batrachia ; the 

 same phenomenon in the cotyledons or plumule of some seeds. In 

 these cases the superficial area of the parts is excessively developed, 

 and the inclosing organs not being proportionately enlarged, a 

 convolution necessary follows. In the first case, the skull ; in the 

 second, the alveolus ; in the third case, the seed-envelope, restrain 

 the expanse of the contained j)art, which would otherwise follow 

 increase of growth-force. 



3. Absolute loss of Groiuth- Force. — This will follow defective 

 nutrition, produced by inability of the animal to obtain heat and 

 food requisite to that end. This is supposed to be due, according 

 to the view hereafter proposed, primarily to deficiency of intelli- 

 gence, in failing to adapt habits to changed physical circumstances, 

 and secondarily to the unfavorable influence of such changed cir- 

 cumstances. The extinction of highly specialized types, which 

 has closed so many lines of animal types, will be accounted for by 

 their less degree of plasticity and want of capacity for change un- 

 der such changed circumstances. Such changes consist of modified 

 topography and temperature, with irruptions of many new forms 

 of life by migration. The less developed forms would be most 

 likely to experience modification of structure under a new order 

 of things, and paleontology teaches that the predecessors of the 

 characteristic types of one period were of the less specialized forms 

 of that period which went before. 



Thus is explained the fact that, in following out the line of 

 succession of animal forms, we have constantly to retrace our steps 

 from specialized extremes (as osseous fishes, tailless Batrachia, 

 song birds, etc.) to more generalized or simple forms, in order to 

 advance beyond. 



4. The complementary diminution of growth-nutrition follows 

 the excess of the same in a new locality or organ, of necessity, if 

 the whole amount of which an animal is capable be, as I believe, 

 fixed. In this way are explained the cases of retardation of char- 

 acter seen in most higher types. The discovery of truly comple- 

 mentary parts is a matter of nice observation and experiment. 

 Perhaps the following cases may be correctly explained. 



A complementary loss of growth-force may be seen in absence 

 of superior incisor teeth and digits in ruminating Mammalia, where 



