6 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



are quicker and more sensitive conductors than undif- 

 ferentiated 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 certain group of reflexes --the so- 

 called instincts. Instincts are defined in various ways, 

 but no matter how the definition is phrased the mean- 

 ing seems to be that they are inherited reflexes so 

 purposeful and so complicated in character that no- 

 thing short of intelligence and experience could have 

 produced them. To this class of reflexes belongs 

 the habit possessed by certain insects of laying their 

 efs on the material which the larvae will afterwards 



oo 



require for food. When we consider that the female 

 fly pays no attention to her eggs after laying them, we 

 cannot cease to wonder at the seeming care which 

 nature takes for the preservation of the species. How 

 can the action of such an insect be determined if not 

 by mysterious structures which can only be contained 

 in the ganglion-cells? How can we explain the in- 

 heritance of such instincts if we believe it to be a 

 fact that the ganglion-cells are only the conductors 

 of stimuli ? It was impossible either to develop a 

 mechanics of instincts or to explain their inheritance 

 in a simple way from the old standpoint, but our con- 

 ception makes an explanation possible. Among the 



