1878.] REV. S. J. WH1TMEE ON THE HABITS OF FISHES. 133 



When swimming in a placid condition, the anterior portion of the 

 dorsal fin in fishes is seldom elevated ; hence the spines which occupy 

 this position are laid back more or less closely, and are often scarcely 

 visible 1 . The anal fin is also often not fully expanded ; but I have 

 not usually seen this so marked as in the dorsal. On the least fright 

 up goes the dorsal, and the spines are at once elevated. As an ex- 

 ample of how slight a cause will suffice to produce this change, I 

 may mention that, before writing the last sentence, I rose from my 

 desk and lightly tapped the front of my aquarium. The anterior 

 dorsal fins of its inhabitants (previously laid back) were instantly 

 elevated, and all assumed the attitude of attention. Under the 

 influence of great anger or fear, such as would be caused by the 

 presence of a carnivorous fish in the aquarium, the dorsal fin is 

 raised to its extreme height, and the spines, both of the dorsal and 

 anal fins, are very prominent. The scales all over the body are 

 also more or less raised, and with them, of course, any other dermal 

 appendages the particular fish may possess. This causes it to 

 assume larger proportions than under ordinary circumstances. 



I believe the spines are elevated under the influence of fear as well 

 as by anger. I was once trying to catch a Tetrodon nigropunctatua 

 which was in my aquarium, when it inflated itself and elevated the 

 fine spines with which its body was covered, and which were pre- 

 viously buried in its loose and flabby skin. This of eourse was 

 under the influence of fear. And this appears to give a hint as to 

 the purpose for which this fish and those of the genus Diodon inflate 

 themselves. 



When I have observed fishes chasing each other, apparently in 

 playfulness rather than anger, I have often seen them swim at each 

 other with open mouths as if to bite. But when they have appeared 

 to intend a serious attack they have always turned suddenly round 

 and lashed at one another with the caudal fin. I believe serioas 

 fighting is always done with the tail. And from their anatomy 

 one would naturally expect this to be the chief mode of attack in 

 most fishes. 



I incidentally mentioned this way of fighting by fishes in a paper 

 recently sent to the Society, in which I described an attack made 

 by some small fishes on an Antennctrius 2 . These little things were 

 evidently in great dread of their carnivorous neighbour. But, 

 like small birds in presence of a bird of prey, they could not keep 

 at a distance, but continually tried to torment it. In attacking it 

 they always took care to strike at its posterior part, although this 

 was protected by a block of coral. I said, in the paper referred to, 

 that this mode of attack by the tail ought to be very effective in the 

 case of au Acantkurus, and that it may account for the armature of 

 the Acronuridse. 



In connexion with this subject I will mention a thought which 

 has often occurred to me as to the chief purpose served by fishes' 



1 Drawings of fishes usually represent them with all the fius fully expanded 

 and the spines prominent ; but this is not their ordinary condition. 



2 See P. Z. S. 1875, p. 545. 



