1064 THE THEORY OF TRANSFORMATIONS [ch. 



a system of hyperbolas *. The old outline, transferred in its integrity 

 to the new network, appears as a manifest representation of the 

 closely alUed, but very different looking, sunfish, Orthagoriscus mola. 

 This is a particularly instructive case of deformation or transforma- 

 tion. It is true that, in a mathematical sense, it is not a perfectly 

 satisfactory or perfectly regular deformation, for the system is no 



Fig. 525. Diodon. 



Fig, 526. Orthagoriscus. 



longer isogonal; but nevertheless, it is symmetrical to the eye, and 

 obviously approaches to an isogonal system under certain conditions 

 of friction or constraint. And as such it accounts, by one single 

 integral transformation, for all the apparently separate and distinct 

 external differences between the two fishes. It leaves the pa-rts 



* The coordinate system of Fig. 526 is somewhat different from that which 

 I first drew and published. It is not unlikely that further investigation will 

 further simplify the comparison, and shew it to involve a still more symmetrical 

 system. 



