252 ROYAL SOCIETY OF CANADA 
In all these cases, when full maturity is reached, the psychic dif- 
ference is not great. The rabbit and the cavy are about on the same 
mental plane and so are the pigeon and the fowl. 
They all illustrate general laws of development and the study of these 
creatures, somewhat low in the vertebrate and psychic scale, seems to me 
to throw much light on the problems of psychology, viewed not as 
human psychology alone, but in the broadest possible sense. 
