610 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



ordinates the movements of the various rays of the starfish (Romanes, A. R. 

 Moore). Next there arises a segmented nervous system, in which, in addition, 

 there forms a central system of ganglia, and in which each segment of the 

 body contains collections of ganglia cells joined by nerve fibers running 

 lengthwise through successive segments. This is a step towards increasing 

 integration. The segmented plan, on which the nervous system is built, per- 

 sists even in the highest organisms. At first the developing central ganglia are 

 of relatively little importance, because the different parts of which the or- 

 ganism is composed are still largely independent of one another. 



Under favorable conditions certain cells and tissues retain the power to 

 live independently, even in the highest organisms, but the ability of parts of 

 the organism to lead their own existence and to restitute the whole organism 

 when separated from the rest, diminishes step by step ; likewise, the power to 

 regenerate organs or other portions of the animal lessens or may become 

 entirely lost. Concurrently with this development and with the increasing 

 complexity of tissues and organs and their greater tendency to coordination, 

 the central nervous system gains in importance and becomes more intricate. 

 However, it is not until the latter has reached a certain stage, after a differen- 

 tiation of the cortex has taken place in the forebrain, that thoughts may form 

 on the basis of sense impressions and that the ability to abstract and syn- 

 thesize becomes possible, and that there thus develops the psychical-social 

 individuality in its most complete form. The cortex arises first in reptiles. 



The phylogenetic development of the social-psychical individuality is thus 

 paralleled by the evolution of the nervous system with its increasing com- 

 plications, such as an increase in differentiation and segregation of parts of 

 nerve cells and fibers in localized areas, the formation of certain projection 

 systems connecting the peripheral sensory receptor organs with subcortical 

 ganglia and the connections of the latter with the peripheral effector organs 

 and later with the cerebral cortex. It is also paralleled by the development 

 of systems of association fibers within the cortex of the brain, the forma- 

 tion of distinct ganglia within the more or less diffuse neuropil, and by the 

 stratification and individualization of the cortex. At the same time there 

 seems to remain everywhere a less well defined neuropil, consisting of 

 shorter neurons and collateral nerves; it infiltrates the other, more localized 

 parts diffusely and to this tissue has been attributed, by Herrick, the integra- 

 tive activities of a lower type, as for instance, the maintenance of the tonus 

 in more primitive organisms, as well as those of a higher type. According to 

 this view, these latter processes would not essentially be localized, as are 

 certain sensory projection nerve fiber systems, the motor nerve fiber systems 

 with which they connect, and, although less obviously, the association fiber 

 systems. Hand in hand thus with the differentiation and individualization of 

 certain separate mechanisms, new connecting, centralizing systems develop. 

 In accordance with the increasing complexity of the organization in general, 

 the number of the primary simple reflexes increases, the complexity of their 

 interaction likewise increases, and they then extend and become converted 

 into complex, associated, conditioned reflex systems. The effect eventuating 



