Law of Proenvironment 231 



also the segregation of increasingly large brain areas for recep- 

 tion of stimuli, and, much more so, for increasing formation 

 of accessory correlating centers, where compound resultant 

 responses can most quickly and perfectly be started, that 

 stimulate the organism to rapid satisfied action. 



In applying the above views to proenvironal reaction in 

 the simpler Metazoa we may first cite the detailed studies of 

 V. Uexkull (83) on the sea-urchins. He has demonstrated 

 the presence of a diffuse nervous system external to the shell, 

 and of a radial internal system. Each little ganglionic area 

 of the former system, that is associated with a movable spine 

 or a pedicellaria, can so stimulate either of the latter that one 

 of them can respond individually, and proenviron a line of 

 movement even when isolated from the shell. In other words 

 each minute nerve-center for a spine, and each nerve center 

 for a pedicellaria, can act as a definite receptive and responsive 

 area. But further, these indi\adual centers are all linked up, 

 so that "they cause the various organs to work in harmony, 

 usually assisting to perform certain necessary functions." 



Thus, if debris falls upon the sea urchin, the pedicellarise 

 seize it, break it into bits, and wdth the aid of the spines and 

 the cilia remove it from the body. Small animals coming 

 into contact with the sea urchin are seized by the pedicellarise 

 and held, till they are grasped by the slowly moving tube feet 

 and spines, and by them carried to the mouth and eaten. When 

 the sea urchin is attacked by an enemy, the spines all bend 

 toward the region of the attack, presenting a serried array of 

 sharp points to the advancing enemy. 



V. Uexkull has therefore designated this animal "a republic 

 of reflexes," and so it can well be quoted as a transition type 

 between the lower and the higher animals. But such trans- 

 ition involves more complicated results than are seen in plants 

 or in lower animals, and suggests first a simple summation 

 of resultant stimuli. Thus the presence of particles of debris 

 start chemotactic, geotactic, and thigmotactic stimuli, all of 

 which become compounded into a resultant response. But 

 weight of the particles to be removed and their relative hard- 

 ness start apogeotropic and thigmotropic stimuli that together 

 become a resultant response, and this along with the former 

 resultant constitute a compounded resultant that effects break- 

 age of the particles and the casting free of them. Definite 

 quantities or tubes of energy therefore, of varied quality, 

 acting on the ganglionic centers, are gradually compounded 



