December 15^ 1905.] 



SCIENCE. 



799 



The fish remained at the bottom of the aqua- 

 rium and went slowly to take refuge under a 

 tile which served as a shelter. It was then 

 three o'clock in the afternoon. The next day 

 at the same hour I found it in a package of 

 Jussieua plants which was floating on the 

 surface of the water. 



In order to examine my fishes closely, I re- 

 moved the plants and observed that Nos. 1 

 and 2 did not appear to be at all influenced 

 by the operation which they had undergone. 

 Only No. 2, deprived of its pectoral and ven- 

 tral fins, seemed unable to move easily. No. 

 3 moved the posterior portion of its body 

 quicldy, and by uninterrupted lateral shakes 

 was able to turn, rise, fall and swim forward, 

 but with much less rapidity and ease than the 

 others, which, with a stroke of the tail, darted 

 like arrows without needing to strike the 

 liquid again in order to. advance. The third 

 fish ended by learning to replace his caudal by 

 the movements of the dorsal and anal, which 

 increased a little in size, doubtless from the 

 exercise. 



One more experiment remained to determine 

 the functions of the fins and of the air- 

 bladder. All the fins except the caudal were 

 cut off of one fish. The creature thus mu- 

 tilated at first appeared undecided, like No. 

 3, and moved slowly at the bottom of the 

 aquarium; but the next day I saw him swim 

 rapidly and execute with agility all his usual 

 evolutions. The only noticeable peculiarity 

 was that in order to keep himself in position 

 he caused his only fin to vibrate rapidly and 

 constantly, and that these vibrations communi- 

 cated a trembling to the entire body. The 

 equilibrium was, therefore, still preserved, and 

 the air-bladder did not cause the fish to turn 

 belly upwards, although he maintained him- 

 self at the bottom of the water, in the middle 

 or at the surface, experiencing in consequence 

 a series of different pressures. My friend, 

 the learned Belgian professor, F. Plateau, so 

 well known by his experiments on insects, and 

 who encouraged me to publish these studies, 

 writes to me that he teaches his pupils that 

 locomotion in most fishes is effected by flexions 

 of the entire caudal portion of the body, and 



that the undulations of the odd fins (dorsal, 

 anal and caudal) serve only to give more pre- 

 cision to the general movements of locomo- 

 tion; and that, save in exceptional cases, the 

 functions of the pairs of fins are almost inap- 

 preciable. I am happy to see my observations 

 accord with the ideas of a savant whose name 

 carries weight. 



When my fishes swim slowly or remain 

 motionless, the caudal fin executes very clean 

 helicoid movements (skulling). This fin ap- 

 pears, therefore, to be, not indispensable, but 

 extremely useful in swimming. Progression 

 forward is due to the alternate flexions of 

 the tail, that is to say, of the part of the body 

 situated behind the anus, as everybody knows ; 

 but, according to the observation made on 

 No. 3, it is evident that the fin which ter- 

 minates it lends it a very powerful aid, for 

 both rapidity and uniformity of motion. With 

 regard to the function of the pectorals, I have 

 remarked that when the fishes which possessed 

 them remained stationary they, nevertheless, 

 continued to move these fins rapidly, and that 

 the latter appeared to be intended to produce 

 currents in the water to renew the portions of 

 this fluid which had already yielded their 

 oxygen to the gills and remained charged with 

 carbonic anhydride. 



It is evident that these experiments on a 

 single species and on so small a number of 

 fishes are insufficient to determine in a gen- 

 eral manner the role of each kind of fin, and i 

 I publish them only to instigate other more 

 varied studies, particularly by means of fishes 

 provided with well-developed fins. With re- 

 gard to those vertebrates which possess only 

 the caudal, it is known that the shape of their 

 body, especially of the posterior portion, per- 

 fectly explains direct progression. 



Before closing this article, I wish to call 

 attention to a fact which perhaps has not yet 

 been observed, or at least not published. The 

 amputated dorsal fin and the two pectoral fins 

 have grown out again to a great extent. It is 

 probable that the mutilated fishes continued 

 mechanically to make use of the stump which 

 remained to them, doubtless with a small frag- 

 ment of the fin, and that under that action the 



