RADIATED WEAVER. 145 



from a line and a half to two lines in length ; 

 but such is the muscular power possessed, that it is 

 with difficulty one of the spines can be pressed 

 doAvn, so long as the fish survives. 



Spines, in some form or other, appear the most 

 ordinary manner in which a weapon is provided. 

 In those fishes we have alluded to, they have ge- 

 nerally been furnished by some peculiar modifica- 

 tion of other parts of the structure used for necessary 

 purposes ; but in a great many species we shall find 

 the same kind of weapons placed on different parts 

 of the body. What an admirable defence the 

 jagged back and tail of the thorn-back skate affords ; 

 while in some of the s^me family we find the tail 

 armed with a long spine, sometimes plain and some- 

 times serrated ; an example of the latter structure 

 vdW be found in our Plate Y., and it occurs in very 

 many other genera ; in many of these, we are 

 inclined to believe that the tail can be wielded, and 

 a wound inflicted. 



Some of the dog-fish, forming the genus Spina^^ 

 of the family of the sharks, have also very strong 

 and beautifully rounded spines; these are placed 

 sometimes at the posterior base of the dorsal, and 

 sometimes near both first and second dorsal fins ; 

 and it is possible that with these a wound may 

 be given designedly. A good example of this 

 form of defence may be seen in our native Spinxa 

 acanthias^ also in many foreign species, and which 

 we may further illustrate by a closely allied fi:^h, 

 the 



