ON THE CAUDAL AND ANAL FINS OF GOLD-FISHES. 



261 



normal teleost the case is quite different (Fig. 24). Here the two 

 lines suddenly converge behind the ventral fins and unite with each 

 other, in which state it continues down to the end of the body. The 

 preanal folds are embryonic structures; they vanish as the embryo 

 advances in development. 



General Observations. — From what has been said about the 

 skeletal element of the paired anal and caudal fins, it is sufficiently 

 evident that they are accompanied by somewhat profound structural 

 deviations from their normal type. It seemed to me exceedingly 

 doubtful if such deviations were purely accidental productions of 

 artificial selection, designed after the breeder's fancy and devoid of 

 any significance whatever from the standpoint of comparative mor- 

 phology. The examination of embryos has clearly proved that the 

 paired state of those fins is anticipated from a very early embryonal 

 period, being laid out as two longitudinal folds. The idea that the 

 law of abbreviated heredity had here been active in shifting the 

 artificially acquired paired condition of the anal and caudal fins into 

 the embryonal period, seems to be untenable. On the other hand, 

 the most plausible explanation lies in assuming that under certain 

 circumstances certain fishes have the anal and caudal fins laid in a 

 double state and that breeders have taken advantage of this fact in 

 producing their double-tailed forms. 



The development of double folds as " Anlage " for the anals 

 and the caudals, I regard as a case of reversion to the primitive state. 

 It stands in favor of the view entertained by St. Mivart, Thacher, 

 Dohrn, Balfour and Mayer with regard to the origin of vertebrate 

 limbs. These authors claim, in contradistinction to the well-known 

 gill-arch theory of Gegenbaur, that the paired fins of fishes were 

 derived from originally continuous lateral folds and further that the 

 anal as well as the ventral portion of the caudal fin arose through 



