992 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [12] 



Teleosts and one of the EolocepJialL The complete absorption of the 

 tail of the larval Anura is also interesting in this connection, and, as 

 already suggested by Huxley, may account for the development of the 

 styliform, unsegmented nrostyle which terminates the vertebral col- 

 umn in adult Anura, as an ossification of the proximal part of the 

 chordal axis of the tail of larva. 



It may be that the intestine terminated much farther posteriorly in 

 the most primitive forms of the Vertchrata, when they were more worm- 

 like, with a terminal anus. With the degeneration of the body-cavity, 

 and its specialization anteriorly, the caudal region probably became 

 rudimentary, and was either partially absorbed, or became specialized 

 into a portion of the body the sole office of which was to aid in locomo- 

 tion. With this acquisition of a new function the degenerating tail has 

 passed through a remarkable series of changes, which left the posterior 

 axial elements to atrophy more or less, while their hinder appendages, 

 which were more or less well preserved, became intermediary supports 

 for appendicular rudder-like organs or a fin-skeleton developed in the 

 skin. Folypteriis* shows how far back and near the tail the body-cav- 

 ity may extend. As extremes of the opposite kind may be cited the 

 entire group of the Heterosomata and the case of Orthagoriscus, fully dis- 

 cussed in another place. This last-named case of extreme reduction or 

 degeneration surpasses even the specialized condition found to obtain 

 in the tail of Hipimcampus. 



In Gastrostomtts we meet with a condition of the vertebral column 

 resembling its condition in the allied form Uurypharynx, writing of 

 which it has been said by Vaillant that its body seemed in its progress 

 to the tail to lose its bones and be converted into a sort of tough and 

 gristly appendage. While such a statement is hardly true of Gastrosto- 

 mu,s, the caudal portion of the axial skeleto)) is exceedingly degenerate, 

 the vertebral segments long but without distinct upper and lower 

 arches, and so little ossified as to consist of very little else than the 

 membranous notochord, which actually does appear to constitute the 

 extreme terminal part of the axis of the body. This condition there- 

 fore recalls the structure of the tail of Ghimcera monstrosa, with its cau- 

 dal axis prolonged as a filament, or that of the singular type called 

 iStylephorHs by Shaw.t The caudal filament of SUflephoru-s is, however, 

 twice the length of the body, or 22 inches. The -'caudal" fin consists 

 of five epaxial spines, if Shaw's figure is trustworthy. The form there- 

 fore has no true hypaxial caudal rays, as in nearly all Teleosts; in fact 



* Polypterus also has the ribs passing outward through thfe lateral muscles to the 

 skin anteriorly, somewhat as in the sliarks, while they girth the hody-cavity posteri- 

 orly, as iu other fishi's. The character which Balfour iusisted upon as one which dis- 

 tinguished the sharks from Ganoids and Teleosts, therefore, has no great taxonomic 

 value, unless this trait of Folypterux should be found to be characteristic of all of the 

 Crossopterygiaus and not be found in any other fishes. 



tShaw's Naturalists' Miscellany, VII. PI. 274. 



