AUTHOR'S PREFACE 



THE dependence of human affairs upon the nervous 

 system of man is so absolute that it was inevitable, as 

 soon as this relation was understood, that the activities 

 of the simpler animals should be interpreted as though 

 these creatures were miniature human beings. That such 

 interpretation was carried far beyond its legitimate 

 bounds, even by the scientifically trained, is now admit- 

 ted on almost all sides, but it is no easy or simple task to 

 ascribe to this movement its proper bounds. That these 

 bounds are vastly more restricted than has usually been 

 supposed is certain. An approach to a clearer under- 

 standing of what they are is assured through the appli- 

 cation of experimental and quantitative methods to the 

 questions concerned rather than by a continuation of the 

 older more purely observational procedure. It is from 

 this standpoint that an attempt has been made in this vol- 

 ume to portray the elementary nervous system as it 

 exists in the simpler animals and in the simpler parts of 

 the more complex forms. It is believed that this treat- 

 ment of the subject may help in the solution of the gen- 

 eral problem by removing once and for all some of the 

 old misunderstandings concerning the nervous system 

 and by inviting the student's attention to new methods of 

 attack. 



The subject matter of the volume is drawn almost en- 

 tirely from the three simpler phyla of the multicellular 

 animals, the sponges, the crelenterates, and the cteno- 

 phores. This is intentionally done for the reason that the 

 activities of such animals as the echinoderms, worms and 



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