FORM AND GROWTH IN FISHES 397 



It must be added, however, that this conclusion applies only 

 to external form, because Kellicott has shown that in the case 

 of the dogfish, certain internal organs (brain and viscera) differ 

 in their rates of growth in much the same independent way as 

 in higher vertebrates. 



FORM 



A study of table 3 (p. 389) reveals some interesting points. It 

 will be noticed that the values of the constants c for the length 

 of the body, head, and tail, and for width (but not for depth) 

 are surprisingly alike for the different species. For example, 

 the values for the body-constant vary in the different species 

 between 0.424 and 0.530, which is a fair agreement considering 

 the different relations of the body limits in the different species. 

 The values for the tail-constant show a still better agreement, 

 the variations here being between the extremes of 0.273 and 

 0.334. In fact, if an average is taken for each constant, the 

 extreme variation on either side of this average is approximately 

 10 per cent, while most of the values lie well within this range. 



This general similarity of form in the different species is, of 

 course, not unexpected. On account of the relatively dense 

 medium in which fishes live, and the resistance it offers to move- 

 ment, it seems reasonable to expect that, in general, all fish 

 will present a form that offers the least resistance, and yet have 

 the necessary mechanism for rapid motion, preying, defense, 

 and so on. Individual variations in the degree of development 

 of the various functions are bound to result in modifications of 

 this generalized fish-form, and an expression of this variation 

 is given in the figures of table 3. 



A corroboration of my conclusion as to this general similarity 

 of form is found in the work of Parsons ('88), who has studied the 

 contours and areas of about fourteen teleosts and several cetaceans 

 from the point of view of the naval engineer. He has found 

 that if the areas of the cross sections of a teleost are plotted 

 against their distances from the tip of the snout, the resulting 

 area curves are surprisingly similar for all species. He states 

 that ''the position of the greatest area of cross-section is fixed 



