XVII] THE COMPARISON OF RELATED FORMS 



'51 



in its integrity to the new network, appears as a manifest 

 representation of the closely allied, but very different looking, 

 simfish, Orthagoriscus mola. This is a particularly instructive 

 case of deformation or transformation. It is true that, in a 

 mathematical sense, it is not a perfectly satisfactory or perfectly 

 regular deformation, for the system is no longer isogonal; but 



Fig. 381. Diodon. 



Fig. 382. Orthagoriscus. 



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 parts 

 near to the origin of the system, the whole region of the head, 

 the opercular orifice and the pectoral fin, practically unchanged 



