1886.] NATURAL SCIENCES OP PHILADELPHIA. 29 



therefore, this seems to have been very generally employed as a 

 defense of the sluggish against such swifter moving carnivorous 

 animals as may have arisen. One great superiority of the verte- 

 brate type has alwa3's been the superior suitability of its form 

 and motor organs to swift movement, and it seems quite likely 

 that the great variety of mechanically defended lower forms in 

 the earl}' fossiliferous beds, is due to the existence of swift- 

 moving antique vertebrates, which were themselves nearly or 

 quite destitute of hard parts, capable of preservation. Though 

 a later " struggle for existence," between vertebrates themselves, 

 caused the weakest and least active of these to develop armor, 

 yet it was succeeded by a general tendency in this type of life to 

 discard mechanical defenses, and trust to motion for protection. 

 The same has been the case with the actively aggressive members 

 of some of the lower tj^pes, such as the higher mollusks, which 

 have thrown off their armor, and developed other defensive appli- 

 ances. 



Throughout the whole history of the organic realm one prin- 

 ciple holds good. There has been a continued evolution of more 

 rapid and varied powers of motion. To this, every advance in 

 organization has tended, while the hindrances to speed and flexi- 

 bility have been successively discarded by the higher forms of 

 life. In correspondence with this has been the development of 

 mentality, since mentality, as outwardly displayed by the animals 

 below man, is indicated by a greater intricacy of motions, in 

 combination with ambush and concealment. For the attainment 

 of the highest possible speed and strength, little mentality was 

 requisite, and brain development is manifested rather by intricac}'- 

 than by speed of motion or rather by that well-ordered correla- 

 tion of rest and diversified motion suited to the best good of 

 the organism. Yet we must regard mentality as rather the effect 

 than the cause of motor evolution. Probably the power of diver- 

 sified motion appeared first, while the exercise of any new power 

 of this kind acted as an agent in the development of the brain. 

 In other words, the evolution of the brain is a consequence of 

 that of the body not the reverse. 



