18S().] PKOCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 71 



ON THE VALUE OF THE FIN-RAYS AND THEIR CHARACTERIS- 

 TICS OF DEVELOPMENT IN THE CLASSIFICATION OF THE 

 FISHES, TOGETHER WITH REMARKS ON THE THEORY OF DE- 

 GENERATION. 



By JOIIIV A. KVDKIS. 



As stated by me in various notices heretofore publisliod, the most 

 l)rimitive arrangement of the rays of fishes is a coHtinuous one, such as is 

 2)ermanentli/ retained by the Dipnoilns.* Since this conclusion lias been 

 reached, further investigation and comparison has shown that in the 

 most primitive types of the fins there are no interradial spaces, such as 

 are found between the rays of the fins of Teleosts. This general truth, 

 completely verified by embryology, seems to lead to results of some sig- 

 nificance in taxonomy. For instance, the two groups, Di[)noi and Holo- 

 cephali, which have the least difterentiated system of rays in the fins, 

 are also amongst the lowest and most archaic in their organizations, for 

 in neither are there any true interradial si)aces such as are found in the 

 members of the Ganoid and Teleostean series. 



The Dipnoi, as respects the fins, are nearer to the Teleostei than to 

 the Squali, because their membranous fin-rays (horn fibers of authors), 

 or actinotrichia, properly speakingy are in a single series on either side 

 of the mesoblastic core of the fins, the same as in Teleostean embryos, 

 and are not made up of several superimposed rows, as in the Sharks. 



Since the foregoing was written, a memoirt of the greatest value, by 

 Dr. Meyer, has appeared on the development of the median fins of 

 Elasmobranchs, in which it is also shown that in the embryos of this 

 series there is but a single row of actinotrichia on either side of the 



*1. Au Outliue of a Theory of the Development of the unpairofl Fins of Fishes. 

 Am. Nat., Jan., 1885, pp. 90-97, 8 tigs. 



2. The Development of the Ray.s of Osseons Fishes. Am. Nat., Fob., 188.'), pp. "200- 

 204, 5 figs. 



3. On Certain Features of the Development of the Salmon. Proc. U. S.Nat. Miis., 

 188."), pp. I.'SG-IG^, pi. XII. (The word actinotrichia was proposed for the first time in 

 this paper as <a general term for the " horn fibers " or embryouie fin-rays of fishes.) 



4. On the Availability of Embryological Characters in the Classification of the 

 Chordata. Am. Nat. , Aug. and Sept., 1885, pp. 815-819 and 903-907. 



5. Tlie Archistome-Theory. Am. Nat., Nov., 1885, pp. 1115-1121. 



fi. On the Origin of lletcrocercy and the Evolution of tlie Fins and Finrays of 

 Fishes. In press. 12 plates. 



N. B. — The new terms which will bo met with in the following are defined in the 

 context. Fuller definitions will be fonnd in the author's papers cited above. 



t 7. Die Uupaaren I'Tossen der Selachier, von Paul Meyer. Mitth. ans der zoolog. 

 Station zn Neapel, VI., pp. 215-281, pis. 15-19. (Dated latter part of May, 1885.) 



