32 
and locomotion. If we examine two such extremely 
dissimilar creatures as the eel and the sunfish, we 
see the peculiar caudal expansion dispensed with in 
both, and the dorsal and abdominal appendages unit- 
ed together as a continuous border. Now nothing 
can seem so little in relation, one to the other in 
structure as the two fishes here mentioned. ‘The 
modification of the accessory fins is, however, the 
same, the difference is the elongation of the column 
into the serpentine length in the eel, and the contrac- 
tion of it, into the dimensions and shape of an oblate 
spheroid in the sunfish ; the usual skeleton mechan. 
ism that stands in the stead of the organs of pro- 
gression and support, being reduced to mere rudi- 
ments. Ishall advert to two or three other instances 
unlike the two preceding examples in which these 
accessory organs, are specially arranged and expand- 
ed-to meet peculiarities in habit. ‘The first I shall 
advert to, is the gymnetrus, a fish totally deprived of 
the anal fin. The dorsal fin is removed forward to 
the crown of the head, where it stands erect like a 
fan. The caudal is similarly expanded upward in 
an erect fan-like form at the upper angle of the tail 
vertebra, the intermediate space all along the back, 
being a continuous soft-rayed dorsal fin. (Eaample 
Gymnetrus fal. Cuvier’s Animal Kingdom : Fishes Grif. 
Ed. page 209.) The next fish I refer to, is the pter- 
acles, in which the dorsal and anal fins are of im- 
mense development, being each twice the breadth of 
the body of the fish, the tail, and pectoral fins pre- 
serving the ordinary dimensions. (Example pteracles 
