24 MEMOIR JOHN BARCLAY. 



mains of animals, that at one time had been its in- 

 habitants, when it presented a different aspect and 

 had different climates from what it has now. " It 

 was by comparative anatomy," he was wont to ob- 

 serve, " that Harvey made his immortal discovery of 

 the circulation of the blood, and Asellius exhibited 

 the existence of the lacteai vessels ; and to the dis- 

 section of a frog we owe the discovery of the Gal- 

 vanic fluid/' and the publisher of this Work, when a 

 boy attending the High School of Edinburgh, has 

 often carried frogs to the Doctor, for the purpose of 

 the varied experiments with which he was then en- 

 gaged. 



Comparative anatomy also points out many rela- 

 tions that subsist between the varieties of function 

 and organs between the varieties of organs and in- 

 stincts, and between the instincts and external cir- 

 cumstances. It points out many relations between 

 the form and habits of species, between the different 

 organs of sense and the objects that invite .or threaten 

 them from without; between certain appearances 

 in the brain and the rapid or slow development 

 of the instincts; between the organs of defence 

 and attack, and the corresponding dispositions ; 

 and between the ratio of the volume of brain, 

 compared with that of the spinal marrow, and the 

 natural sagacity common to the species. While, 

 on the other hand, to prevent our ascribing too 

 much to the organs, and supposing that the in- 

 stincts, the habits, and characters of animals are, in 

 all cases, to be regulated by them, it furnishes us 



