982 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [2] 



I. — Terminology. 



The names applied by different authors to tbe initial or larval stages 

 of development of the Teleosteau tail differ so greatly in their etymolo- 

 gies and their implicntions, that it is desirable not only to consider the 

 terms hitherto proposed, but also, in order to be more precise, to add 

 certain ones in order to designate phases of developmeut and conditions 

 of structure which have not been heretofore recognized. 



The term arcMcercy and its adjective form arcMcercal will therefore 

 be introduced here in order to define thecylindroidal, worm-like caudal 

 end of Ichthyopsidous larva' before they acquire median finfokls. 



Jeffries Wyman* in 18G4 proposed the term protocercal to designate 

 the larval condition of the tail of liaia when it had acquired median tin- 

 folds. This term seems to imply that this primar\' form of the tail of 

 larval fishes precedes in the order of time the subsequent conditions, 

 or that it is the first stage of the evolution of the caudal fin. Tills term 

 was adopted in the same sense by Wilder in his article, " Gar pikes, 

 old and young," Popular Science Monthly, XI, 192,1877, where the con- 

 dition of the tail of the larva? of LcpMosteus was considered. 



A, Agassizt in 1877 considered the subject anew, and in an essay 

 071 the development of the tail, which is of great value from an embryo- 

 logical standi)oint, proposed the term ?(''/?/oe/irr/m7for the same condition 

 implied by the word protoeercaU for the reason that young fishes in 

 this stage showed a uniform and continuous development of the median 

 fin-fold over the end of the body, very similar to the condition which is 

 permanently characteristic of the vcMtical fins of the Leptocaixlians. 

 If it IS true, however, that the median fin -folds of the latter contain 

 rudimentary cartilaiiinous basal rays or tlieir rej)reseutatives, the com- 

 l)arison and the choice of tlie name are slightly at fault, and is really not 

 as appropriate as the one previously proposed by Wyman. Inasmncli, 

 tlierefore, as the terms fiiphycercal, heteroccrcal, &c , refer to definitely 

 understood structural conditions of the tail in adult forms, it seems not 

 inappro])riate, undesirable as it is to add another to the number of ex- 

 isting terms, to propose a new one to designate the symmetrical, eradi 

 ate condition of the continuous or discontinuous median tin-iold or folds 

 of larval fishes, and which, like the terms applied to the description of 

 the tail of the adult, shall have reference solely to structure and not 

 imply anything as to an hypothetical parallelism with a lower type, nor 

 anything respecting a supi)osed order of evolution. Such a term it is 

 not difficult to choose, if we bear in mind that the earliest form of the 

 caudal fiu is little or nothing more than a fold of the skin which is com- 

 posed entirely at first of epiblastic tissue, and that it does 'not incbule 

 rays even of the. most rudimentary kind. The term, therefore, which 



* Observations on the developmeut of JRaia hatis, Mem. Amer. Aco^d. Arts aud Sci- 

 ences, 1864. 



t On the young- stages of Osseous Fislies, Proc. Am. Acad. Arts and Sciences, XIII, 

 p. 123. 



