THE SUNFISH AND THE SPARROIV 57 



cavities enclosed by the gills are called gill-pouches. 

 Note the gill-rakers, short and blunt, on the first gill 

 arch. Note also, on the under side of the flaps turned 

 back, delicate red gill-like structures covered by a mem- 

 brane. These are the false gills. The true gills are 

 organs by means of which the fish 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 

 carbonic 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, show- 

 ing 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 

 microscope 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 



