412 THE SENSORIAL FUNCTIONS. 



of the salamander. During the first periods of 

 their existence, these animals are perfectly 

 aquatic, breathing water by means of gills, and 

 having all their organs formed on the model of 

 the fish. Their nasal cavities are not employed 

 for respiration at this early period, nor even for 

 some time after they have begun to take in air, 

 which they do by the mouth, swallowing it in 

 small portions at a time, and afterwards throwing 

 it out in bubbles by the same channel. But when 

 they quit the water, and become land animals 

 M ith pulmonary respiration, the nostrils are the 

 channels through which the air is received and 

 expelled ; and it is here also that the sense of 

 smell continues to be exercised. 



We know very little respecting the seat of the 

 sense of smell in any of the invertebrated 

 animals, though it is very evident that insects, 

 in particular, enjoy this faculty in a very high 

 degree. Analogy would suggest the spiracles as 

 the most probable seat of this sense, being the 

 entrances to the respiratory passages. This 

 otfice has, however, been assigned by many to 

 the antennae; while other entomologists have 

 supposed that the palpi are the real organs of 

 smell*. Experiments on this subject are at- 

 tended with great difficulty, and their results 

 must generally be vague and inconclusive. 



* On the subject of this sense in insects, See Kirby and 

 Spence's Introduction to Entomology, vol. iv. p. 2-49. 



J 



