272 PROCEEDINGS OF THE AMERICAN ACADEMY 



fins of some of the earlier Ganoids in which the fin rays are very 

 numerous, as, for instance, the Platygnathus of the Old Red. These 

 characters are represented in the Ganoids of to-day both in Ceratodus 

 and Protopterus ; indeed even the Blennies, Eels, Murenid^e, and 

 Ophididae of to-day may be regarded as types of these embryonic 

 stages, of which Phaneropterus with its confluent dorsal and caudal 

 is a representative among the older fossils. But in the one case the 

 fin rays are the permanent rays, while in the other the [embryonic] 

 fin rays disappear with the appearance of the permanent osseous fin 

 rays, as I have shown in my paper on the early stages of Lepido- 

 steus.* The same conditions are repeated also in the young stages of 

 that genus. t 



As regards the formation of the dorsals, the posterior dorsal is the 

 first to be differentiated ; in the embryos of the osseous Fishes the 

 anterior dorsal appearing only subsequently, and either independently 

 or connected with the posterior one. In those fishes which have 

 these fins separated in the adult, the dorsals are usually united in the 

 earlier stages, but if the anterior dorsal is of a peculiar type, as, for 

 instance, in Lumpus, Trachypterus, and Lophius, the anterior dorsal 

 becomes separated at an early stage, sometimes even while still in the 

 egg, from the posterior dorsal. We can therefore assume that as far 

 as the dorsals are concerned a continuous median fin still connected 

 with the caudal is the earliest embryonic type of fin. 



The next stage of development is a type in which the caudal is well 

 separated from the dorsal and anal embryonic fold, with a continuous 

 single dorsal ending finally by the differentiation of the dorsal into 

 one or more independent dorsals. The formation of abnormal types 

 of anterior dorsal to form structures adapted to special uses, as in 

 Lophius, is an embryonic feature, and this development of the dorsal 

 may exist either as a separate dorsal, or the anterior rays of the single 

 dorsal may be developed to an extraordinary degree, forming immense 

 filaments, as in Argyreiscus, Blepharis, and many other fishes. 



This anterior dorsal also may exist only in the embryonic stage, as 

 is the case in Fierasfer and Trachypterus. The anal is usually well 

 developed before the appearance of the ventrals, except in the cases of 

 those genera in which the ventrals take an extraordinary development 



* Proc. Amer. Acad., 1878, XIII. p. 65. 



t In my next paper on bony Fishes, I hope to treat of the transformation of 

 the median fins of osseous Fishes from their embryonic stage to that of fins 

 with permanent osseous rays. 



