154 



THE PLACOID BRAIN. 



versy of this nature, — I spend a little more in indicating 

 what I deem the proper ground on which the standing of the 

 earlier yertebi*ata should be decided. To the test of brain 1 

 nave already referred as all-important in the question : I 

 would now refer to the test of what may be teimed homolo- 

 qical symmetry of organizatiov 



