STUDY OF FISHES 139 



usual is the use of the pectoral fins for crawling on, as in the 

 angler, or as parachutes (in the flying fishes). 



The point to make clear here if possible by direct observa- 

 tion is that the movements of the paired fins do not usually 

 count for much in locomotion. But they are (in many cases, at 

 least) absolutely essential in enabling the fish to keep its normal 

 position in the water. 



(3) The unpaired fins act as vertical keels in the great majority 

 of fishes ; they steady the swimming, preventing wobbling. 

 Observation will show that they can be raised or lowered as is 

 needed. This may be compared to the use of a movable keel 

 in some yachts. In the pipe-fishes and sea-horses the unpaired 

 dorsal fin is very mobile, and is the chief swimming organ. 



(C) Breathing Movements. Observation of the minnows or 

 sticklebacks in the aquarium shows that the mouth is opened and 

 shut many times in a minute, and that there is a corresponding 

 closing and opening of the external aperture of the gill-chamber. 

 The water sucked into the mouth-cavity is forced over the gills and 

 passes out beneath the gill-cover. In the fishes named the breathing 

 movements are unusually rapid ; the number should be counted 

 in other cases, such as trout and gold-fish. When a gold-fish is 

 (ignorantly or carelessly) kept in water from which much of the 

 dissolved oxygen has been removed (by being used up), the rate 

 of respiration increases abnormally. The fish is beginning to 

 suffocate. This is not an edifying spectacle, but is a common one. 



SECOND STUDY: THE EXTERNAL CHARACTERS OF FISHES 



It is often possible to get a number of perfectly fresh specimens 

 of some small fish, such as trout, sprats, whiting, which can be 

 used in class for the study of external characters. This kind of 

 study is of use as an observational exercise, as a lesson in 

 precision. To master some things thoroughly gives the pupils 

 confidence ; it enables them to see more in things. 



In studying the external features attention should be paid to 

 the following points in particular : 



(a) Shape. The typical shape suited for rapid locomotion, the 

 flat shape suited for life on the floor of the sea, the eel shape 



