CHAPTER VIII 

 THE ORGANS OF SENSE 







HE Organs of Smell. The sense-organs of the fish cor- 

 respond in general to those of the higher vertebrates. 

 The sense of taste is, however, feeble or wanting, and 

 that of hearing is muffled and without power of acute discrimina- 

 tion, if indeed it exists at all. According to Dr. Kingsley (Vert. 

 Zool., p. 75), "recent experiments tend to show that in fishes the 

 ears are without auditory functions and are solely organs of 

 equilibration." 



The sense of smell resides in the nostrils, which have no re- 

 lation to the work of breathing. No fish breathes through its 

 nostrils, and only in a few of the lowest forms (hagfishes) 

 does the nostril pierce through the roof of the mouth. In 

 the bony fishes the nostril is a single cavity, on either side, 

 lined with delicate or fringed membrane, well provided with 

 blood-vessels, and with nerves from the olfactory lobe. In most 

 cases each nasal cavity has two external openings. These may 

 be simple, or the rim of the nostril may be elevated, forming a 

 papilla or even a long barbel. Either nostril may have a papilla 

 or barbel, or the two may unite in one structure with two open- 

 ings or with sieve-like openings, or in some degenerate types (Tro- 

 pidichthys} with no obvious openings at all, the olfactory nerves 

 spreading over the skin of a small papilla. The openings may be 

 round, slit-like, pore-like, or may have various other forms. In 

 certain families of bony fishes (Pomacentridce, Cichlida, Hexagram- 

 ides), there is but one opening to each nostril. In the sharks, 

 rays, and chimaeras there is also but one opening on either side 

 and the nostril is large and highly specialized, with valvular flaps 

 controlled by muscles which are said to enable them "to scent 

 actively as well as to smell passively." 



In the lancelet there is a single median organ supposed to 



"5 



