THE SUNFISH AND THE SPARROW ii 



breathes under water. Note the fish continually gulping 

 water. This water with air dissolved in it passes through 

 the mouth into the gill-pouches and out under the operculum. 

 Thus the dissolved air in the water comes in contact with the 

 gills, passes through the delicate gill membranes and into 

 the blood, which runs in many fine capillaries through the 

 gills, while at the same time the blood itself gives up carbon 

 dioxide, which passes out through the gill membranes into 

 the water. In this way the blood is purified. 



Make a drawing from lateral view of the sunfish, showing 

 and naming the parts studied. 



Professor Needham gives the following directions for 

 seeing the flow or circulation of the blood in the caudal fin 

 of a fish : 



"Wrap the fish in a wet towel, leaving the caudal fin 

 exposed, and place it on a low box beside the microscope, 

 with >its caudal fin extending across the center of the micro- 

 scope stage. Spread the fin out flat on a glass slip upon the 

 stage, so as to bring a thin portion of it into the field, and 

 examine it with low power. If the fish refuses to lie quietly, 

 pour a little chloroform on the towel near its mouth. 



"Observe the conspicuous, dark, irregular pigment cells 

 scattered throughout the epidermis of the fin. 



"The larger blood-vessels are of two kinds: (i) arteries, 

 bringing blood out into the fin, and (2) veins, conveying the 

 blood back to the body again. The smaller ones are the 

 capillaries connecting the arteries with the veins, and dis- 

 tributing the blood throughout the tissues of the fin. 



"Observe that the blood consists of a fluid plasma, in 

 which float numerous corpuscles. Observe that the blood 

 appears red in the arteries and veins, where the corpuscles 

 are accumulated, but only slightly reddish or yellowish in 

 the capillaries, where the corpuscles form but a thin layer. 



"Does the blood travel faster in the arteries and veins, 

 or in the capillaries? 



