TRANSFORMATIONS. 165 



the centre of the disc, now along one arm, now 

 along another, and sometimes vividly illuminat- 

 ing the whole outline. 



Mention may fittingly be made in this chapter 

 of transformations in the shape of the body as a 

 whole, selecting from the very numerous in- 

 stances two of the most striking. 



Of these the most familiar will be that of 

 the sea-horse (Hippocamjms). The change in 

 shape here is not perhaps very considerable, 

 but it is quite unique. The fish in swimming 

 moves in a vertical position, and is driven along 

 by rapid vibrations of the dorsal fin. The tail- 

 fin has disappeared, and the tail has become 

 transformed into an organ of prehension. The 

 external scaly armour has developed exceedingly, 

 and at the expense of the internal skeleton. It 

 forms a delicate bony framework, which may be 

 likened to filagree work. Further modifications 

 which the fishes of this genus may undergo may 

 be studied in the " Story of Life in the Seas," 

 where a picture will be found showing the extra- 

 ordinary mimetic resemblance to seaweed, which 

 some species develop for protective purposes. 



Our second example of transformation of the 

 external form is furnished by the wonderful 

 sun-fish (Orthagoriscus). This fish has the appear- 

 ance of having undergone the amputation of the 

 hinder end of the body, just behind the dorsal 

 fins. One is naturally puzzled to account for 

 such an extraordinary modification, but it seems 

 to be associated with, and has, perhaps, resulted 

 from its peculiar diving habits. It is the ogre 

 which haunts the night of the deep seas, and 



