1890.] The Homologies of the Fins of Fishes. 419 
constituted the first intelligent application of the structural char- 
acters of fishes’ fins to their systematic arrangement, which was 
made. 
Subsequently the paleontologist McCoy,’ observed that in 
some extinct fishes the vertebral column did not enter the supe- 
rior part of the caudal fin, but continued directly to its middle 
base, and terminated without modification, the rods supporting 
the fin radiating equally and symmetrically above and below to 
the extremity. This type of fin he called diphycercal. 
Later, Huxley ® studied the development of the caudal fin in 
the salmon, and showed that although the caudal fin proper is 
heterocercal, some of the terminal vertebrae enter the base of the 
superior lobe, thus having a partially heterocercal structure. 
Cope, in 1871, reviewed the structure of the caudal fins of 
recent and extinct fishes. He stated that the diphycercal type 
(which he termed isocercal in ignorance of McCoy’s paper) is the 
primitive condition of this region, preceding the homocercal in 
embryonic history. He showed that it persists in various modern 
fishes, as in the Lepidosiren and Polypterus, and among Telesto- 
mata, in the eel-like types, inthe Gymnarchidz, and in the Ana- 
canthini, and in the last-named supporting a heterocercal caudal 
fin. He also showed that in various living isospondylous fishes 
besides the salmon, a partially homocercal condition persists, nota- 
bly in the Notopteride. 
A valuable contribution to this subject is that of E. T. New- 
ton,™ who has worked out some of the developmental stages of 
the sprat, and brings together the works of several earlier writers 
upon the subject. No notice is taken in this pamphlet of the 
writings of Cope, Wilder, and other American naturalists who 
have at various times observed or reasoned out the steps by which 
the primitive vertical fold becomes a highly differentiated caudal 
fin. 
31 Annals Magaz. Nat. Hist., 1848, p. 304. 
32 Quarterly Journal Microscop. Science, 1859, P. 33- 
33 Transactions of the American Philosophical Society, XIV., 1870, pp. 452, 453- 
34 On Fishes’ Tails, by E. T. Newton, F.G.S. Ext. from the Journal of the Queckett 
Microscopical Club, July, 1882. 
