208 GENERAL EVOLUTIOI^. 



necessary when inherited in the foetus for the construction (by 

 conversion) of tissues and organs like those of the parent. 



,y^ That this is a partial explanation of inheritance, is rendered 

 probable from the fact that the types of structure presented by 



\ the nervous centers express the grade of the animals possessing 

 them far more nearly than those of any other organ or set of or- 

 gans. If the brain, like other organs, develops by intelligent use, 

 it can not be doubted that this relation of its development to 



I grade is not accidental, but that grade-structure * is an expression 

 of its capacities, physical and mental. 



V. o:n" intelligent selection. 



As neither nse nor effort can be ascribed to plants, and as we 

 know that their life history is much more dependent on their sur- 

 roundings than is that of animals, we naturally look to the physi- 

 cal and chemical causes as having a prime influence in the origina- 

 tion of their type-structures. Without greater familiarity with 

 the subject, I will not attempt to say how far the various degrees 

 of growth-force possessed by parent plants, located under the influ- 

 ence of meteoric and other surroundings, and preserved, destroyed 

 or restricted by natural selection, may account for the characters 

 of their successors of the present period. But other agencies simi- 

 lar to use, that is, automatic movements, may be also introduced 

 as an element in the argument. The movements of tendrils seek- 

 ing for support may be here considered, and, as Dr. Asa Gray has 

 pointed out, have consequences similar to those of use in animals. 

 When the tendril seizes a support, growth-force is located at the 

 point of contact, for the tendril increases considerably in thick- 

 ness. 



Among animals of the lowest grade, movement must be quite 

 similar to those of plants, or automatic from the start, and not 

 even at the beginning under the influence of will. Evidence of 

 will is, however, soon seen in the determinate movements of many 

 of the Protozoa in the seizing of food. With will necessarily ap- 

 pears a power of choice, however limited in its lowest exhibitions, 

 by the lack of suggestive metaphysical qualities, or the fewness of 

 alternatives of action presented by surrounding circumstances, to 

 animals of low and simple organism. We can, however, believe 



^ Grade growth-force is not regarded here or elsewhere as a simple form of 

 energy, but as a class of energies, which are the resultants of the interference of 

 mind (i, e., consciousness) with simple growth-force. (Ed. 1886.) 



