302 J. K. Thaeher — Median and Paired Pins. 



for drawing. The very striking similarity to the uniserial archip- 

 terygiuni raised the question whether the median fins, at any rate the 

 dorsal and anal fins, might not have arisen from the same archiptery- 

 ginm. The result of my investigations was a decided negative. 

 It has been absolutely proved that they did not so originate, and 

 the way in which they did originate has been clearly shown. 



While then, on the one hand it has been shown that the develop- 

 ment of a pair of fins, whoso skeleton consists of a series of 

 parallel rays clothed on each side with a layer of muscle, as a 

 specialization of the lateral folds (raetapleura of Ray Lankester) of 

 AniphioxHs, contains no steps which have not been taken in the same 

 animals in the case of the median fins, so also it has been shown that 

 the development, of the ventral fins and the pelvic girdle of sharks 

 from such a series exhibits no processes or kinds of change which are 

 not also exhibited in the median fins of those same fishes. When we 

 contrast the changes from a series of parallel rays to the completed 

 ventral fin of the shark, as it has been given above, with the changes 

 which Gegenbaur supposes to have made it out of the archiptery- 

 gium, namely, the stripping ofi" of every one of the median rays, for 

 no sign of them is ever found in the ventral fins aside from the Dipnoi, 

 and the slipping off of the orad portion of the rays to immediately 

 articulate with the shoulder girdle, I hardly think that those changes 

 of his will appear so well evidenced as these changes which I believe 

 to have taken place. And when the utter darkness that covers the 

 development of the arehipterygium itself (for it does not seem fair to 

 the arehipterygium to make much account of the suggestion of 

 Gegenbaur respecting the branchial arches, Unters., Hft. iii, p. 181, 

 note) is contrasted with the familiar changes which would have 

 brought these Selachian fins out of the lateral folds Ainphioxus, I 

 hardly think the advantage can lie with the arehipterygium. 



Homodynamism of Median, and Paired P'ins.* 



Let us compare the ventral with the dorsal fins, say in Mustelus 

 cams. 



* Since this paper was written, I have found a paper of Humphrey's on the Homo- 

 logical Relations of Mesial and Lateral Fins of Osseous Fishes, Journ. of A_nat. and 

 Phys., Nov., 1870. Here a comparison between the fins in question is made in the 

 case of the Pike, and the " Iliac " or " Pubic " bones in osseous fishes are assimilated 

 to the interneural spines or to the prominal part of them. Goodsir had made some 

 earlier comparisons without valuable result. See Anatomical Memoirs, vol. ii, p. lOtJ. 



