232 Causes and Course of Organic Evolution 



into one complex resultant, that exhibits itself in orderly mo- 

 tion in one given direction. 



As illustrations of animals with more aggregate or condensed 

 nervous system, we may next select Thysanozoon and also 

 planarians that Loeb has studied. His sectioning experi- 

 ments {60: '72) indicate that the anterior or richly ganglionated 

 and correlated head part, as well as the posterior or poorly 

 ganglionated and correlated part of the nervous system, can 

 receive, correlate, and summate into resultant proenvironal 

 response several environal stimuli that act on it. But the 

 posterior part is more sluggish and less perfectly linked to- 

 gether than is the anterior. Such is partial proof that the 

 evolving brain ganglia are condensed and equihbrated sum- 

 mators of all afferent stimuli, while the body ganglia are less 

 perfect. The results got by Loeb with Planaria iorva would 

 suggest that it has a more diffuse capacity for reception and 

 correlation of stimuli than has Thysanozoon, and so that it 

 is intermediate between the latter and the sea-urchin in physi- 

 ological elaboration. 



At this point consideration may shortly be given to the 

 evolution and relative action of individual nerve cells, and 

 further of motor and inhibitory nerve centers, or ganglia, a 

 subject that is further treated in a later section (p. 238). 



The fundamental peculiarity of a nerve cell is that it can 

 receive a stimulus from one center of cell stimulation, and 

 reflect or direct it to some other center, so as to cause change 

 in the latter, or also in other cells around. But a further and 

 highly significant function of such a nerve cell is that, when 

 two or more stimuli reach it, simultaneously or in rapid suc- 

 cession, from different centers, the summated action of these 

 may all be cumulated into one resultant that causes a definite 

 proenvironal response in the same or some other centers. This 

 inherent and unique capacity we have considered to be due 

 to the action of a highly perfect and transformable exhibition 

 of energy, the cogitic, which effects a linking together of highly 

 comj^lex colloid molecules, so as to start a compounded reac- 

 tion along proenvironal lines. 



But it must further be noted that along with such com- 

 pounded reaction there is involved, in increasing complexity, 

 as we ascend the scale of animal life, the explanation of mem- 



