THE BODY OF A FISH 



243 



a vertebrate. There are 37,000 known species of vertebrates. 

 These species are divided into five groups or classes : Pisces, or 

 fishes ; Amvhibia, or amphibians ; Reptilia, or reptiles ; Aves, 

 or birds; Mammalia, or iTKnnials. 



skeleton../ \ / ^^^V_\ skeleton. 



htatb.4— ^O J ^ G^-feSS 



V J \ v -/-KidCtiey 



nerve ^V^-co ^/^ \ m.—^.-Jieorr'b 



cord ^- 11-^ V_l^ 



invertebrate/ ver-tebrette 



Cross section of an invertebrate and of a vertebrate. In what ways are they similar? 

 In what ways do they differ ? 



Laboratory Exercise. Adaptations in a fish. How is the body of 

 the fish fitted for life in the water? Mention three different adapta- 

 tions for swimming. Watch the fish carefully and locate its organs 

 of locomotion. How many single fins are there? How many paired 

 fins? 



Try to discover what fins are used in forward motion, in turning, in 

 moving backward. Is the body used in locomotion. How is each 

 particular fin adapted or fitted to do its work? 



What structures do you find on the surface of the body ? How are 

 these structures placed with reference to each other? Feel the body 

 of the fish. What adaptation for protection exists here? Note the 

 color both above and below. Remembering that many of the enemies 

 of the fish are below him and some above, explain how the animal 

 receives protection from its color. What are the principal adaptations 

 for protection in the fish ? j 



Look at the living fish carefully and observe the movements of the 

 mouth. What is the relation of the movement of the mouth to that of 

 the operculum, the flap which covers the gills? Note position and 

 color of the gills. What gives them this color? Put a few grains of 

 carmine in the water in front- of the mouth of the fish. Trace the 

 course of the carmine. Where does it come out ? What gas is in the 

 water? How does the fish use this gas? How might this gas come in 

 contact with the gills? Write a paragraph and illustrate with a 

 diagram, showing how a fish breathes. 



The body. The long, spindle-shaped body, pointed at the 

 anterior end, with its smooth surface, admirably adapts a fish 

 for swimming. Mucus 1 secreting cells in the skin, and the position 



1 Mucus: a sticky slippery secretion found on the membranes lining various 

 body cavities, as the nose or mouth. 



