NOTES ON ICHTHYOLOGY. 23 



Nature,") because it states the results of experiments, which I have 

 myself repeated, better than any words of mine could do. It says that 

 in most fish " beside the great fin the tail, we find two pairs of fins upon 

 the sides, two single fins upon the back and one upon the belly, or rather 

 between the belly and the tail. The balancing use of these organs is 

 proved in this manner : of the large-headed fish, if you cut off the 

 pectoral fins, i. e., the pair which lies close behind the gills, the head 

 falls prone to the bottom ; if the right pectoral fin only be cut off, the 

 fish leans to that side ; if the ventral fin on the same side be cut away, 

 then it loses its equilibrium entirely ; if the dorsal and ventral fins be 

 cut off, the fish reels to the right and left. When the fish dies, that is, 

 when the fins cease to play, the belly turns upwards. The use of the 

 same parts for motion is seen in the following observation upon them 

 when put in action. The pectoral, and more particularly the ventral, 

 fins serve to raise and depress the fish ; when the fish desire to have a 

 retrograde motion, a stroke forward with the pectoral fin effectually 

 produces it ; if the fish desire to turn either way, a single blow with the 

 tail the opposite way sends it round at once ; if the tail strike both 

 ways, the motion produced by the double lash is progressive, and 

 enables the fish to dart forwards with an astonishing velocity. The 

 result is not only in some cases the most rapid, but in all cases the most 

 gentle, pliant, easy, animal motion with which we are acquainted. 

 However, when the tail is cut off the fish loses all motion, and gives 

 itself up to where the water impels it. The rest of the fins, therefore, so 

 far as respects motion, seem to be merely subsidiary to this. In their 

 mechanical use, the anal fin may be reckoned the keel, the ventral fins 

 the outriggers, the pectoral muscles the oars, and if there be any 

 similitude between these parts of a boat and a fish, observe that it is 

 not the resemblance of imitation, but the likeness which arises from 

 applying similar mechanical means to the same purpose." 



In reference to the foregoing, one error needs correction, and one 

 observation may be added. The error is in asserting that if the tail be 

 lost in the fish it loses all motion. This it does not do. The posterior 

 parts are still exercised as if the tail still remained, and the resulting move- 

 ment is what anglers term a " wobble," but, nevertheless, a progressive 

 movement. The addition is one the truth of which anyone may verify 

 by watching the progression of the sticklebacks in a tank at the Royal 

 Westminster Aquarium. The fish distinctly advance by a series of 

 jerks caused by the pectoral fins. The tail has nothing to do with 

 progression, and seems only to make a quivering movement to maintain 

 equilibrium. I know of no other fresh-water fish with the same 

 peculiarity. 



