Pisces. 161 



doubts their keenness of sight, let him fish for trout or black 

 bass before rendering his verdict. The sense of touch 

 seems well developed. Numerous fishes have tactile bar- 

 bels about the mouth, as the catfish, sturgeon, and codfish. 

 The lateral line is considered a sense organ. There is an 

 internal ear, but it does not appear that fishes hear ordinary 

 sounds made out of water, like human speech, unless they 

 are loud ; on the other hand, fishes have a keen perception 

 of any sound vibrations that are directly transmitted to the 

 water, such as splashing in the water, noises made by the 

 grating of oars in the oarlocks or by hard objects striking 

 the bottom or sides of a boat. The semicircular canals are 

 now understood to be connected with a sense of equilibrium. 

 Smell is probably pretty well developed, in some fishes at 

 least. The nostrils have nothing to do with respiration in 

 any fishes below the lungfishes. The nostrils do not open 

 into the mouth, but are simply openings into a cavity 

 around which the nerves of smell are distributed. Some 

 fishes have a single nostril on each side. In others, as in 

 the perch, there are two openings on each side. The two 

 nostrils of one side connect with a common cavity, the 

 water entering through one aperture and leaving through 

 the other. The sense of taste is probably less distinct. 



Excretory Organs of the Perch. The gills excrete car- 

 bon dioxid. For the removal of nitrogenous waste matter, 

 there is a pair of slender red kidneys which extend the 

 whole length of the body cavity. They can be seen 

 through the dorsal wall of the air bladder. There is an 

 enlargement at the anterior end in front of the air bladder. 

 At the posterior end there is a tube, the ureter, to convey 

 the excretion to the exterior ; this duct joins a small uri- 

 nary bladder and opens just back of the opening of the ovi- 

 duct, so that the three openings at this place are, in order 



