XVII] THE COMPARISON OF RELATED FORMS 1063 



start this series with the figure of Polyprion, in Fig. 521, we see that 

 the outlines of Pseudopriacanthus (Fig. 522) and of Sebastes or 

 Scorpaena (Fig. 523) are easily derived by substituting a system 



Fig. 521. Polyprion. 



Fig. 522. Pseudopriacanthus alius. 



of triangular, or radial, coordinates for the rectangular ones in which 

 we had inscribed Polyprion. The very curious fish Antigonia capros, 

 an oceanic relative of our own boar-fish, <Jonforms. closely to the 

 peculiar deformation represented in Fig. 524. 



Fig. 523. Scorpaena sp. 



Fig. 524. Antigonia capros. 



Fig. 525 is a common, typical Diodon or porcupine-fish, and in 

 Fig. 526 I have deformed its vertical coordinates into a system of 

 concentric circles, and its horizontal coordinates into a system of 

 curves which, approximately and provisionally, are made to resemble 



