170 ANIMAL FORMS 



is forced through the gills, with all their delicate filaments, 

 and now, laden with oxygen and nutritious substances al- 

 ready absorbed from the coats of the digestive tract, it 



FIG. 106. Dissection of a bony fish, the trout (Scdmo). a.bl., air-bladder ; an., anal 

 opening; at/., auricle; gl.st., gills; gul., esophagus; int., intestine; kd., kidney ; 

 lr., liver; l.ov., ovary; opt.l., brain ; py.c., pyloric 'coeca ; sp.c., spinal cord ; spl., 

 spleen ; st., stomach ; v., ventricle. 



travels on to all parts of the body, continually unloading 

 its cargo in needy districts and waste matters in the kid- 

 neys before returning once more to the heart. 



163. The senses of fishes. The habits of fishes indicate 

 that they know considerable of what is going on in the 

 outside world, and their well-developed sense-organs show 

 the degree of their sensitiveness. A share of this informa- 

 tion comes through the sense of touch, which is distributed 

 all over the surface of the body, chiefly in the more ex- 

 posed regions sometimes especially provided with fleshy 

 feelers, like those on the chin of the catfish. 



The sense of smell appears to be fairly developed, as is 

 that of hearing ; but there is no evidence of a sense of taste. 

 A few fishes chew their food, and may possibly taste it, but 

 there are others that swallow it whole, and in all there are 

 relatively a few nerves going to the tongue or floor of the 

 mouth. 



