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 conductability 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 poly- 

 pes 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. 



