368 THE SENSORIAL FUNCTIONS; 



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 por- 

 tions at a time, and afterwards throwing it out in 

 bubbles by the same orifice. But when they quit 

 the water, and become land animals with pul- 

 monary 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 invertebrate 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 respi- 

 ratory passages. This office 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 attended wTth great difficulty, and their results 

 must generally be vague and inconclusive. Those 

 which Mr. P. Huber made on bees seem, however, 

 to establish, with tolerable certainty, that the spi- 

 racles are insensible to strong odours, such as that 

 of oil of turpentine which is exceedingly offensive 

 to all insects. It was only when a fine camel-hair 

 pencil containing this pungent fluid was presented 

 near the cavity of the mouth, above the insertion 



* On the subject of this sense in insects, see Kirby and Spence's 

 Introduction to Entomology, vol. iv, p. 249. 



