PORCUPINE DIODON. 143 



cies which roam openly, and do not naturally conceal 

 themselves among rocks or the forefcts of sea-weeds, 

 or among the mud and sUme of the bottoms, there 

 are many species which have different and accessory 

 parts of the form strongly knotted and spined, and 

 which we can scarcely view in any other light than 

 as accessory parts of defence. Thus many of the 

 PercidcG have their gill-covers strongly spined and 

 serrated. The first and second rays in the dorsal 

 fin of the same family are often also very strong and 

 rough ; and every one accustomed to fish for the 

 rommon perch of the British lakes and rivers, must 

 nave observed the powerful manner in which these 

 are erected, when the fish is first raised from the 

 water; it is evidently used instinctively as a de- 

 fence, and by this means it is one of the few species 

 which we can keep in company with the pike. The 

 heads of the Cotti are all strongly armed with spines, 

 with which they are able to wound severely, by 

 turning or wriggling. Such is also the case with 

 the Scorpoence, and the Triyla or gurnards. In the 

 weavers, forming the genus TroLchinus^ they are 

 exhibited in the 



