348 



ZOOLOGICAL SOCIETY BULLETIN. 



SOFT DORSAL 



SPINOUS 0OR5AU 



.\\\\N 



YELLOW PERCH. 

 Giving the names of the different fins, and showing the pe 



C. Of the vertical or unpaired fins the use 

 of the caudal is most evident, since this fin in 

 conjunction with the caudal end of the body 

 furnishes the propelling force in swimming. 

 It is also the chief fin used in steering, acting 

 like a ship's rudder, and its use as such may be 

 easily observed when the fish is swimming 

 slowly. The caudal fin may be used also in 

 maintaining the equilibrium, in this respect 

 supplementing the efforts of the paired fins. 

 This use is best seen in very deep-bodied fishes 

 such as the butterfly-fish, {Chactodon). 



The principal use of the dorsal and anal 

 fins in the ordinary type of fish seems to be 

 to prevent the body from slipping sidewise 

 through the water when the stroke of the cau- 

 dal is made. When these fins are removed the 

 fish wriggles very noticeably while swimming. 

 These fins may have also a direct use in pro- 

 pelling the body, and may aid the pectorals in 

 equilibration. It is not within the scope ot 

 the present paper to discuss the varied special 

 uses of fins by which certain fishes are enabled 

 to fly, crawl, skip, attach themselves to stones 

 or seaweeds, etc. 



A glance at the results of experiments on 

 the removal of fins may be interesting. When 

 one of the pectoral fins is removed the fish 

 tends to turn on its side. In the short deep- 

 bodied type of fish this is very pronounced. In 

 the killifish, (Funduliis hcterocUtus) it is not 

 very noticeable excepting at first, for in a short 

 time the fish learns to keep its balance with the 

 other fins. When both pectorals are removed 

 in a deep-bodied form, such as the scup, {Stcn- 

 otomus chrysops), the fish becomes quite un- 

 able to keep its balance properly, though it can 



swim as rapidly as ever. 

 In the killifish the re- 

 moval of the pectorals, 

 or even of all tlie paired 

 fins, is not so serious a 

 matter ; the only evi- 

 dences of difficulty are 

 seen in the lack of ability 

 to make the more accu- 

 rate movements, and in 

 the fact that at first the 

 fish runs into things ow- 

 ing to its inability to stop 

 quickly. The fish learns 

 in a few days to over- 

 come this latter trouble 

 by a strong sweep of the 

 tail. When the unpaired 

 fins alone are removed 

 :torai fin in motion. the Swimming move- 



ments become labored 

 and progress is much slower although in the 

 killifish the caudal portion of the body is able 

 to accomplish a fair stroke. If all the fins, 

 both paired and unpaired, are removed the 

 killifish is still able to swim by wriggling, and 

 is able to retain its balance by the same 

 method. Naturally all of the movements in 

 such a case are extremely labored. The ex- 

 periment shows, that in some fishes at least, 

 fins are not necessary, though certainly very 

 useful organs. 



In conclusion it must be noted that the fins 

 of fishes are very strongly adaptive structures, 

 and that probably in no two species will ex- 

 actly the same uses and the same combinations 

 of fins to perform the various duties assigned 

 to them, be found to occur. The whole sub- 

 ject will well repay any one who cares to ob- 

 serve the habits and movements of animals. 



Puhlications on Aquatic Life. — Among the 

 publications on aquatic life (referred to on 

 page 339), may be mentioned, Sea Shore Life, 

 by Mayer, The Reptiles and Batrachians by 

 IJitmars, The Reptiles and Batrachians by 

 Eckel and Paulmier, the Salamanders, Frogs 

 and Toads by Sherwood, The Fishes, Turtles 

 and Lizards, by Smith, and The Higher Crus- 

 tacea by Paulmier. With this list to select from 

 we need not remain unacquainted with the 

 aquatic creatures in the vicinity of New York. 



The cuts in this number of The Bulletin, 

 are from photographs by Mr. Spencer and 

 others, and from a number of old lithographs 

 and prints made during the early history of the 

 Aquarium Building, then called Castle Garden. 



