PHILOSOPHY OF ZOOLOGY. 



a. There is no determinate relation observed in the de- 

 grees of perfection of the senses in different animals. Even 

 in the same class, and subordinate divisions of a class, one 

 species or genus may have the organs of smell very fully 

 developed, another those of hearing, a third those of sight, 

 while the other senses may be in a less perfect condition. 

 Even among individuals of the same species, such differen- 

 ces prevail. 



. In judging of the properties of bodies, we seldom rest 

 satisfied with the information obtained by one sense, but em- 

 ploy the results furnished by the others, to correct or 

 strengthen our conclusions. Thus, the organ of touch as- 

 sists that of seeing, and sight aids the efforts of touch. 

 Hence, as the senses mutually assist each other, it is dif- 

 ficult to assign to ach of them the knowledge which it 

 has exclusively communicated. In the case of disease or 

 accident, where one sense has been destroyed, the other 

 senses^ by an increased sensibility, in a great measure sup- 

 ply the defect. Thus, hearing and touch, in many cases, 

 supply the loss of sight, and exhibit striking displays of 

 that compensating or repairing power, to which we have 

 had frequent occasion to refer. 



c. In many animals, where some of the senses exist, aU 

 though we are unable to detect the organs in which they 

 are seated, as is the case with hearing in the annulose ani- 

 mals, it is probable that the deficiency of one sense may 

 be supplied by the sensibility of the remaining ones. 



d. The same qualities in bodies do not produce the same 

 effects on the appropriate organs of all animals. There is 

 a striking difference in the degrees of sensibility ; so that 

 an impression which would be overpowering to one animal 

 is scarcely felt by another, as appears in the case of 

 < ertain sounds, smells and lights. Even sensations excited 

 by the some bodies in different animals, arc dissimilar in 



