FISHES 



249 



Practical Exercise 12. Give a brief definition of a fish that will fit all fishes. 



Using the diagram on page 247, reconstruct a cross section passing through 

 the heart. Use colors for the different organs. 



After watching a fish swim make a diagram to illustrate how a fish moves 

 forward in the water. 



Fishes. All fishes live in the water. They usually secure 

 oxygen by means of gills.- They move by means of appendages 

 called fins. Four of these fins are paired and are homologous to 

 the legs and arms of man. They all possess a vertebral column. 



'Zlasmohrancbi __ 



<3 



ctnoid_ 





PISH£S 



"Butterfly fisS* , _... 



.Dipnoccn 



Order 1. Elasmobranch. Fishes which have a soft skeleton made of cartilage, and exposed 

 gill slits. Examples : sharks, skates, and rays. 



Order 2. Ganoid. Fishes which once were very numerous on the earth, but which are now 

 almost extinct. They are protected by platelike scales. Examples : gars, sturgeon, and 

 bowfin. 



Order 3. Teleostans, or Bony Fishes. They compose 95 per cent of all living fishes. In this 

 group the skeleton is bony, the gills are protected by an operculum, and the eggs are numer- 

 ous. Most of our common food fishes belong to this class. 



Order 4. Dipnoan, or Lung Fishes. This is a very small group. In many respects they are 

 more like amphibians than fishes, the swim bladder being used as a lung. They live in 

 tropical Africa, South America, and Australia, inhabiting the rivers and lakes there. 



Self-Testing Exercise 



Fishes have a (1) made up of irregular-shaped bones. 



This is called the (2) (3). In addition there is an 



exoskeleton which may take the form of (4) . The fish is 



adapted for life in the water by the (5) of its body, 



(6) glands in skin and (7) for breathing. The fish has a 



(8) (9), a (10) chambered heart and a well- 

 defined nervous system consisting of a (11), (12) 



'. . (13), and (14) organs. Many (15) are laid 



but only a (16) reach maturity as the (17) are 



exposed to many (18) and are eaten by other (19) 



as well as other enemies. 



