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GENERAL ZOOLOGY 



aptly described as "taste at a distance." It has been established 

 that organs of smell occur in insects and in other invertebrates 

 such as snails. In the case of insects the antennae and other 

 parts of the body bear olfactory pits in which the receptors lie. 

 In vertebrates, except Cyclostomata, the olfactory organ con- 

 sists of paired sensory areas, which in fishes lie at the bottom of 



Fig. 122. — A, neuromuscular spindle. B, neurotendinous spindle; C, motor 

 end plate, m, muscle; n, nerve; t, tendon. (After Huber and De Witt.) 



ectodermal pits opening to the outside by nostrils, but having no 

 connection with the pharynx. In air-breathing vertebrates these 

 pits are continued backward as nasal passages, opening into the 

 pharynx by internal nares. This condition exists in the frog and 

 in Man. The sensory epithelium lining the passages consists of 

 olfactory cells and supporting cells, the former bearing bristles 

 at their outer ends, while their inner ends continue backward as 

 nerve fibers to form the olfactory nerve. Since olfactory cells 

 arise and remain in the ectoderm, the olfactory epithelium is 



