PROCEEDINQS OF THE 



hy rnnfje of adaplalion or of reaction. The organ or system on 

 which the range of adaptation depends is the one on uhich we 

 must concentrate our attention in tracing back the evolution of 

 the Vertebrate. This organ is the central nervous svetem. There 

 has been no continuous rise in type of the muscular, digestive or 

 respiratory systems. It is the central nervous svstem which 

 determines dominance of any type, and the nervous svstem is 

 the only part of the body which undergoes continuous evolution 

 irom the lowest to the highest forms. The reactions of the 

 highest animals are determined by the nerve-cells and tracts 

 laid down in the embryo and inherited from the parents no 

 new formation or repair being possible after the earliest stages 

 ot loetal life, if indeed at any time. In no case, so far as I am 

 aware, do we find the central nervous system cleared away and 

 laid down afresh in the metamorphosis of" an animal. At various 

 times an animal may breathe by its skin, by gills or by lungs. It 

 may digest its food by means of glands derived from'the epiblast 

 or hypoblast, and indeed digestive ferments may be produced hy 

 almost any cell in the body. It mav excrete waste products by 

 kidneys, intestines, or skin ; but the central nervous system 

 remains the one unchangeable organ, whose function, namely the 

 determination of adapted reactions and therefore of survival 

 cannot be replaced by the vicarious activity of anv other part of 

 the body. ■ ^ 



Looking back as physiologists we mav indeed see that all the 

 main epochs m the evolution of higher forms of life are charac- 

 terized by changes in the nervous system. The first step was 

 taken when the individuals of a cell colony remained in structural 

 connection, so that the consensus partiwn could be maintained by 

 the propagation of molecular changes along the protoplasmic 

 strands between the different cells and no longer depended solely 

 on the diffusion into the surrounding medium of chemical sub- 

 stances which might affect friend or foe alike. By a differentiation 

 among these connecting strands a diffuse nervous system was 

 formed with immensely enhanced rapidity of reaction of the 

 w'hole organism to environmental changes at anv part of its surface. 

 The location of the mouth at the front end of the body, i. e. the 

 one which in the actively moving animal was first exposed to 

 changes in the environment, was attended hy the concentration at 

 this end of the specialized projicient organs of sense, i. e. those 

 whose activity was aroused by changes occurring at some distance 

 from the animal, in a region with which a continuation of the 

 forward progression of the animal would bring it in more intimate 

 relations. The presence of these foreseeinr/ organs at the anterior 

 end necessarily brought in its train a subjection of all other parts 

 of the nervous system to that part, the supra-cesophageal ganglion, 

 which was the first recipient of the afferent impressions from these 

 organs. The rise in type, which has culminated in the production 

 of Man himself, has been determined simply hy a continuous 



