•68 The Mechanistic Conception of Life 



reflexes occur in plants possessing no nervous system, yet in 

 animals where ganglion-cells are present the very existence of 

 the ganglion-cells necessitates the presence in them of special 

 reflex mechanisms. It was therefore necessary to find out if 

 there were not animals in which coordiaated reflexes still con- 

 tinued to exist after the destruction of the central nervous 

 system. Such a phenomenon could be expected only in forms 

 in which a direct transmission of stimuli from the skin to the 

 muscle or direct stimulation of the muscle is possible, in addi- 

 tion to the transmission through the reflex arc. This is the 

 case, for instance, ia worms and in ascidians. I succeeded' in 

 demonstrating in Ciona intestinalis that the complicated reflexes 

 still continue after removal of the central nervous system.^ 



A study, then, of comparative physiology brings out the 

 fact that irritability and conductibility are the only quaUties 

 essential to reflexes, and these are both common qualities of 

 all protoplasm. The irritable structures at the surface of the 

 body, and the arrangement of the muscles determine the 

 character of the reflex act. The assmnption that the central 

 nervous system or the ganglion-cells are the specific bearers of 

 reflex mechanisms cannot hold. But have we now to conclude 

 that the nerves are superfluous and a waste? Certainly not. 

 Their value lies in the fact that they are quicker and more 

 sensitive conductors than undifferentiated protoplasm. Because 

 of these qualities of the nerves, an animal is better able to adapt 

 itself to changing conditions than it possibly could if it had no 

 nerves. Such power of adaptation is absolutely necessary for 

 free animals. 



3. While some authors explain all reflexes on a psychical 

 basis, the majority of investigators explain in this way only a 



1 Loeb, J., Untersuchungen zur physiologischen Morphologie der Tiere, II. 

 Wiirzburg, 1892. 



8 This animal closes the oral opening when we touch it. This is a reflex com- 

 parable to the closing of the eyelid if we touch the cornea. The central nervous 

 sytem of the animal consists of one ganglion. When the latter is removed the 

 oral opening still closes upon mechanical stimulation. 



