1062 THE THEORY OF TRANSFORMATIONS [ch. 



which fossils are subject (as we have "seen on p. 811) as the result 

 of shearing-stresses in the solid rock. 



Fig. 519 is an outUne diagram of a typical Scaroid fish. Let us 

 deform its rectihnear coordinates into a system of (approximately) 

 coaxial circles, as in Fig. 520, and then filling into the new system. 



Fig. 517. Argyropelecua Olfersi. 



Fig. 518. Stemoptyx diaphana. 



space by space and point by point, our former diagram of Scarus, 

 we obtain a very good outline of an allied fish, belonging to a neigh- 

 bouring family, of the genus Pomacanihus. This case is all the more 

 interesting, because upon the body of our Pomacanihus there are 

 striking colour bands, which correspond in direction very closely 



Fig. 519. Scarus sp. 



Fig. 520. Pomacanihus. 



to the lines of our new curved ordinates. In like manner, the still 

 more bizarre outUnes of other fi.shes of the same family of Chaetodonts 

 will be found to correspond to very slight modifications of similar 

 coordinates; in other words, to small variations in the values of 

 the constants of the coaxial curves. 



In Figs. 521-524 I have represented another series of Acantho- 

 pterygian fishes, not very distantly related to the foregoing. If we 



