126 Animal Morphology. 



taste, when it is not suitable aliment for the animal exposed 

 to hunger. These sentinels are specially endowed with 

 the proper appreciation of what is suitable food for most 

 things likely to be placed within their reach, and is one of 

 the forms in which instinct manifests itself. 



In one way or the other, then, it may be said that the re- 

 maining senses are servants to one special sense, over whose 

 door is written, in more than iron characters, " That self- 

 preservation is the first law of nature." This sense is the 

 sense or consciousness of hunger. 



But in birds, as pigeons, rooks, swallows, etc., etc., and 

 in insects, especially the winged insects, as the hymenoptera, 

 it is probable that the par vagum is the seat of a true 

 double sense, and in the sensorium gives two distinct kinds 

 of impression or sensation. The power to retrace their 

 habitations, when far from home, in such small animals as 

 bees, and with eyes constructed upon such singular optical 

 principles, cannot possibly be from sight, nor yet from smell, 

 as they are far inferior in smell to the common imtsca vomi- 

 toria ; but the distances to which they travel, and the cer- 

 tainty of their return, bespeak a guiding power distinct 

 either from smell or sight. 



Pigeons conveyed in hampers, and never once placed in a 

 position of surveying the country across which they will fly 

 in retracing their homes, yet, by winging their flight direct 

 for their old abode, over one hundred miles, indicates a posi- 

 tive guiding sense. Whence do they obtain such know- 

 ledge of distance and .locality? 



It is presumed that the sense of suffocation, or impure air, 

 acts only in man to show him the deficiency of oxygen, and 

 in the asthmatic occasionally other telluric, or atmospheric 

 peculiarities are included. In certain classes of insects and 

 birds this sense is open to stimuli, connected with certain con- 

 ditions of atmosphere, that are always in active operation 



