58 THE POPULAR SCIENCE MONTHLY. 



take in tlie idea of " quantitive reasoning " nor " correlation of forces." 

 The dog is capable of improvement, limited only by his organization; 

 the Hottentot only by liis, and the child, of a large-brained and culti- 

 vated ancestry by his. The difference in these possibilities, however, 

 can only be comprehended upon reflection. The most intelligent ani- 

 mal, or even tlie savage man, bears relations to no surroundings be- 

 yond the mere seeming of things upon the few acres or miles traversed 

 by his race or tribe ; the sun and moon are only what they appear ; 

 they rise just beyond the mountain, and they go down in the forest. 

 The thunder and the tempest are incomprehensible, or are the voice 

 and breathings of an angry God. The philosopher, or man of science, 

 on the contrary, holds converse with all objects, animate and inani- 

 mate ; all peoples and their works, both present and past, upon the 

 surface of the earth. He explores its dej)ths, and calls up before him 

 the generations which peopled it ages on ages past. The microscope 

 brings before him the world of the infinitely small, and the telescope 

 reveals the worlds of space. With the spectroscope he questions the 

 stars, and they give intelligible reply. Such, and a thousand-fold 

 more, are his surroundings ; and it is to express his relations to these, 

 to the complex impressions and sensations to which they give rise, 

 and the reflections and aspirations which they inspire, that the brain 

 of the philosopher must be adequate. 



We Ijave thus noticed the more prominent structural changes as 

 they occur in the nervous system, from its simplest form to its highest 

 development, and also the corresponding psychical manifestations, 

 which each advance in structure rendered possible. We have seen 

 the lowly creature, endowed with its single nerve-centre, and its radi- 

 ating nerve-filaments, expressing all its relations to the outer world by 

 simple reflex action ; and, if, as we should expect, the order of appear- 

 ance in ISTature corresponded with the order of development, for un- 

 told ages all over the silent, ocean-clothed cai'th, no higher form of 

 life, and no higher expression of soul, was present. Gradually, by 

 mar.y a minute addition, in response to improved surroundings and 

 new requirements, new organs appeared, until at length there existed 

 a creature of definite form, with organs of sight and hearing, as well 

 as touch and locomotion. The old ganglionic nerve-system, with its 

 simple reflex movements, was still retained; but, to express the many 

 new relations to the outer world which its gradually-acquired organs 

 made possible, additional nerve-centres were required, and the senso- 

 rixim assumed form and use. The scries of actions performed through 

 its promptings we call instinctive. Then for unknown ages sense- 

 impressions, stimulating to instinctive action, were the highest ex-' 

 pressio'.is of soul upon the slowly-emerging earth. 



But, again, improved surroundings tlie dry earth, with forest, 

 field, and floAver, the brighter sunlight and the purer air, demanded 

 new organs to appropi'iate and \\e\y senses to enjoy; and a race a])- 



