68 COLOUR, FORM, AND MOVEMENT. 



We note (a) their form spindle or wedge shape, 

 (6) their surface smooth, 

 (c) specific gravity that of the water, 

 (c?) great muscular development, 

 (e) fins, 

 (/) air bladder. 



Form. We shall study this in some detail. 



Draw the outline of a fish as seen from above. 



It is a double wedge, with the broadest part a little way 

 behind the front (Fig. I()A) . The head forms a short blunt 



wedge in front, and the 

 body a long tapering 

 wedge behind. It is not 

 unlike the general shape 

 of a bird's body. A 

 consideration of the fish 

 shape with reference to 

 the inward pressure of 

 the water upon the body 

 will show that this tends 

 to push it forward on 

 the slightest muscular 

 effort (see Fig. 10). 



The pressure on the 

 long wedge tends to pro- 

 duce forward slipping, 

 whilst the small wedge 

 presents a cutting edge, 

 removing the resistance 

 which would otherwise 

 be offered in its absence 



Fig. 10. Diagram to show the effect of the 

 pressure of the water upon the body of a 

 typical fish. The median vertical arrows 

 indicate the direction of the resultant pres- 

 sure. See text for full explanation. 



(compare A and B) . 



Note also the absence of all projecting parts or breaks 

 in the even continuity of the body outline. And here 

 it is of interest to recall how animals of fundamentally 



