90 PROCEEDINGS OF THE ACADEMY OF [1893. 



aquarium small, harmless, but very active fishes of other species, in 

 order that the water be kept circulating, and thus aerated for the 

 benefit of the helplessly modified, but most valued tenant. 



These circumstances give, it seems to me, a clew to the explana- 

 tion, not only of the degeneration of the musculature under domes- 

 tication, owing to its enforced disuse, but also some indication of 

 what are the causes of the extension of the fins. The material 

 saved from expenditure in muscular effort may be expended in 

 growth in another direction, and the most advantageous would be 

 that which would increase the surface of the fins, and thus render 

 them useful in dermal respiration. The large vessels and numerous 

 capillaries in the huge tails of very fine specimens of the Kinyiko 

 race, that I have seen, indicate that the caudal fin may possibly 

 serve in a very important way as an adjunct to branchial respira- 

 tion. The question therefore arises, have not the immense fins of 

 the Japanese double-tailed gold-fishes been developed partially in 

 physiological response to artificial conditions of respiration, that 

 were not as favorable as those enjoyed by their wild congeners? 

 That the dorsal, anal and caudal fins may be so modified as to min- 

 ister in an important way to the needs of respiration, is proved by 

 the development of the richly vascular and exaggerated vertical 

 fins of the embryos of foetal Embiotocoid fishes, as long ago shown 

 by Blake, and fully confirmed and elaborated in greater detail by 

 the writer. 



It is also a remarkable fact that the fins and tail of the larvse of the 

 double long-tailed races do not show such characters at once, but it is 

 not until long after the larval stages are passed, that the breeder can be 

 certain of rearing a specimen with a fine long tail, from any given 

 young fish. The fishes are usually upward of two inches in length 

 before the breeder can be pretty sure that the young or half-grown 

 individuals will develop a great length of tail. This fact shows 

 that the long tail was originally acquired very late in ontogenetic 

 development, and is not a larvally apparent differentiation. This 

 circumstance is also unique amongst fishes, and for that matter, 

 almost the exact reverse of what usually takes place, since the young 

 of many marine fishes have certain parts of the fins very greatly 

 produced, only to be absorbed before adolescence is reached. This 

 is the case with the larvse of Lophius and Fierasfer. Only amongst 

 higher animals do we find secondary sexual characters produced at 

 a late period of growth, such as the deciduous horns of the Deer 



