usually not over two ; in otliei' tishes inaiiy of tlicvsc Uheis l)econie iu- 

 volved to form a single ray. Ghimrrni and its allies arc also very i)rimi- 

 tive, their fin rays attaining but a slight ad\ ancc in dcveloinuent beyond 

 what I have denominated the Protopterygian stage of the embryos of 

 Teleosts ; yet even in Chimcera the rays are not absolutely simple, as in 

 the embryonic condition, traces of their coalescenc^e being ])resent. And 

 1 would here insist that the material of which the primitive fibers 

 consists in all fishes, be they Elasmobranchs, Dipnoans, (ianoids, Chi- 

 man^oids, or Teleosts, is similar in its nature and origin and its relations 

 to the primary embryonic layers; that the jtoint where the fin-rays 

 join or ov^erlap their cartilaginous supi)orts in the embryo is homologons 

 throughout the entire phylum of th(^ fishes, andcoustitntes, for thei)cc- 

 torals and ventralsat least, a starting i)oint of equal value with the ar- 

 ticulation of the proximal elements of the limb to the slioulder or pelvic 

 girdle, for the purpose of determining the homologies of Ihe bones or 

 ■cartilages which form the true axial skeleton of the limbs. 



Dr. Giinther, in his valuable monogra]>h on Cnafofhts* (p. .5.')()), says: 

 ^'The dermo-neurals of Cerafodm are not articulated to the extremities 

 of the internenrals, but overlap them for a cousideral)le distance of their 

 length. The shape and arrangement of the dermo haMuals is exactly the 

 same as that of the <lermo-neurals. No ossification takes place in either 

 of them; they consist entirely of cartilage, in which numerons spindle- 

 shaped cells are imbedded, many of these cells being ])roduced at both 

 ends into a very long process (PI. XX XVI, Fig. 7)." These dermo- 

 nenral and haemal elements, as Dr. (riinther calls them, are the exact 

 liomologues of the horn.y fibers of fish embryos, and cannot, I regret 

 to say, be regarded as cartilaginous either in origin oi- histological 

 character. They are allied in constitution to the material in which 

 the ossification of membran<» bone occurs. 



Dr. Giinther also remarks of the fin rays of Ceralodx.s : '-They are 

 exceedingly numerous, four or {\y{\ or more corresponding to a single 

 vertebral segment, and form a double >^enes, one series on each side of 

 the fin. This x>eculiarity, Avhi<;h (kraiodns has in common Avith Lepiflo- 

 sir€7i, reminds ns of those fin rays of Teleosteous fishes which can be 

 more or less completely split into a right and left half." 



This quotation becomes remarkably significant in Ihe light of the 

 facts of development, since we now know that the right and left halves 

 of the rays of Teleosts actually devi^lop in part from the <louble series 

 of embryonic fin-rajs which underlie in a single l;iyer the right and left 

 dermal wall of the fin-foM. The large numViei' of fin-rays to a single 

 segment in CeratoduH likewise no longer apjiears strange ; this condi- 

 tion being simply indicative of the fact that the s])ecialization and the 

 fusion of the embrj^onii- fin-rays into powerful rays has not gone so far 

 as in the more developed and specialized Teleosts, which have all the 



'Pbilos. Transactions, Pt. TI, 1871, \)i\ 511-571. 



n. :\iis. OS — 6G 



