416 



HITCHCOCK'S ANATOMY 



pituitary membrane and furnished with olfactory nerves, which 

 gives them a powerful organ of smell. This cavity, however, 

 has no posterior orifice, its only opening being in front, and 

 the water in it being continually kept in motion by the cilise 

 with which it is lined. In the sharks and rays there is a mus- 

 cular appendage to keep the water in motion, so that Sir 

 Richard Owen says these animals must actively scent (that is 

 search for odoriferous impressions) as well as smell. 



771. Artie ulata. — Crustaceans have the sense of smell, 

 and the central ganglion sends off an olfactory nerve. The 

 Arachnoids can smell without any discoverable organ. So 

 also the Insects. Probably all of the Articulates have this 

 sense, but perhaps without special organs. 



772. Molluscs . — In Cephalopods olfactory organs are made 

 out, but not in the other classes. 



773. R a d i a t a . — No distinct organs for this sense have been 

 found in these animals. But the presumption is that it exists 

 with or without special organs in them all. 



Of the Protozoa the Infusoria clearly evince sensation and 

 volition; but no nervous system has been discovered in them, 

 and though it is quite manifest that they are sensible to the 

 contact with objects and to light, yet there is no evidence that 

 they have the sense of smell. Equally probable is it that it 

 is wanting in the Rhizophoda. 



HYGIENIC INFERENCES IN RESPECT TO THE SENSES. 



774. — 1. Moderation in their Use Required.— All the 

 organs of sensation require to be moderately employed. If 



770. How is it with the sense of smell in fishes? What peculiarity anions: the sharks 

 and rays? 771. Have articulate animals the power of smelling? Have they the organs 

 adapted to it ? How is it probable that lobsters smell ? 772. Can shell-fish smell ? 773. 

 What of animals lower in the sc» ] e ? 



