460 PROGRESS OF SCIENCE IN THE CENTURY. 



some of the many open questions* in comparative 

 psychology. Are there any cases of animal behav- 

 iour which cannot be interpreted without assuming 

 a conceived, as contrasted with a perceived purpose 

 (reason as contrasted with intelligence) ? In what 

 proportion of cases can it be shown that animals util- 

 ise their individually acquired experience, adapting 

 their behaviour in reference to what they have 

 learned, or in relation to some quite novel situation ? 

 To what extent can we interpret the routine life of 

 an animal, say ant or bee, as a series of reflex actions ? 

 How have instincts been evolved? 



Nervous Mechanism. Before we try to make 

 clear the present-day antithesis between the two 

 schools of " comparative psychologists " those who 

 would interpret all the phenomena in objective phys- 

 iological terms, and those who maintain that psychi- 

 cal interpretations are equally essential, we must 

 devote a few paragraphs to stating the generally ac- 

 cepted conclusions in regard to nervous mechanism. 



In the simplest animals (Protozoa), there is 

 irritability and conductibility in the protoplasm; 

 there is nervous function, in short; and there are 

 many interesting modes of behaviour, but there 

 is no distinctly nervous structure. Some of the 

 polypes show in simple form the essential ground 

 plan of all the nervous mechanisms of higher 

 animals. A superficial sensitive cell is connected by 

 a fibre with a more internal nerve-cell or gan- 

 glion-cell, which gives off a fibre to a muscle-cell. 

 If we multiply each of these component parts a 

 thousand-fold, we have a sense-organ receiving 

 stimuli, a sensory nerve transmitting these, a nerve- 

 centre or ganglion receiving, storing, co-ordinating 

 * Science of Life, p. 207. 



