GREA T BRITAIN. 9 



brane, we observe many modifications, some taking on a 

 distinctly osseous character, as in the sheat or scaleless 

 fishes, in which the first ray of the dorsal fin and the upper 

 one of the pectoral are frequently seen as bony spines. 



The component parts of a fin may also become strangely 

 altered, so that it becomes widely different from what is 

 seen in a typical carp or perch. Thus the flying fish, 

 Exoc&tus, has its pectorals modified into an organ or para- 

 chute for assisting it to pass through the air ; our little 

 stickle-backs, Gasterostens, have each ventral fin in the 

 form of a single spine, useful for offensive or defensive 

 purposes, as we perceive in the more developed unicorn 

 fish, Triacanthus, of the Eastern seas. The gurnards, 

 Trigla, have some of their pectoral rays developed into a 

 locomotive and tactile apparatus. In the angler, Lophius, 

 the whole of the fin can be employed as an organ for loco- 

 motion. In a few fresh-water loaches the upper pectoral 

 ray becomes osseous, its extremity becomes flattened and 

 spatulate, enabling it to be employed as a species of spade, 

 so that on the approach of danger it can dig down into the 

 sand and conceal itself with great rapidity. 



Curiously as we see the many modifications of the fins, 

 no less extraordinary are the forms of some of their bodies ; 

 examples exist in the globe-fish, Tetrodon, the flattened sole 

 or flounder, the elongated pipe-fish, or the sword-fish, 

 Xiphias, with its snout modified into a powerful weapon of 

 offence. 



The value of the skin or tegumentary covering of animals 

 as a means of resistance against external injuries, becomes 

 increased should hard substances enter into its composition, 

 and for this purpose many fish are furnished with scales. 

 Scales are developed on papillae on the deep layer of the 

 skin or corium, which, increasing by successive accretions, 



