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Show 1887.] PAIRED FINS OF CERATODUS. 9 described by Huxley (19, p. 49), to which Schneider likens that of the pelvic fin, is constant in its relationships and invariably postaxial. I emphatically deny that structural similarity of the second mesomere of the fore and hind fins suggested by him, while I desire to lodge a protest against the unqualified assertion that (23, p. 523) " das Problem der Entwickelung von Arm und Bein, welches gegen-wartig so vielfach behandelt worden ist, wird dadurch . . . . seiner Ldsung einen Schritt naher gefuhrt." The great variation here demonstrated in the relative number and calibre of the parameres of opposite sides of the normal pelvic fin at least shows that the numerical differences existing between them and those of the so-called irregular fin described at the outset are insignificant. What now of the " branching," to which attention was originally directed by Haswell (15, p. 7) ? In the fin furnished by him all the rays not indicated in the drawing (fig. 1) are simple and unbranched, though somewhat unusually elongated. Many of them are transversely segmented. The question resolves itself into this- Can the irregularities represented in fig. 1 as it stands be shown to exist in a more normal fin 1 Bifurcation of the terminal portion of one or more parameres is no exceptional feature. Giinther (14) and Davidoff (7) have both described it for the pelvic fin, and I figure an example (fig. 7) in which it had attained a marked development. Fig. 5 shows that it is no new peculiarity for the pectoral fin also1. I have seen a dichotomy of the pectoral paramere in one other case, and that in a fin in all other respects normal. The transverse segmentation of the axis of Haswell's fin (fig. 1) is not a whit more remarkable than that of fig. 7 ; while in the fin there represented, as in the pectoral one of fig. 5, irregularities of the preaxial parameres existed which far exceed in abnormality (if such it may be termed) anything forthcoming in the first-named specimen. Briefly stated, Haswell's fin differs most conspicuously from that of the more constant type in respect to the longitudinal cleavage of the axis. This phenomenon has already been recorded by Haswell, and that in a fin which recalls the one here described (15, pl. 1. fig. 6). Albrecht has figured and described (Sitzungsb. d. konig. preuss. Akad. Berlin, vol. xxxii. p. 545, 1886) a specimen of Protopterus (P. annectens) in which the distal half of the axis of the left pectoral fin had similarly bifurcated2. Haswell (15, p. 8), commenting upon the " branching" process which he first described, asserts the belief that " it is reasonable to 1 I found, on examining this specimen minutely, that many of tbe parameres terminated in smaU nodules such as are represented at *. On comparison with the other specimens dissected by me, I a m convinced that similar terminal segments existed in two cases, but that, owing to their delicate nature, they had been for the most part torn away in the process of dissection. The free ends of the rays from which they had been thus removed presented a characteristic truncated appearance, identical with that represented in some of the rays so carefully drawn by Davidoff (7). Putting all together, I incline to the belief that the terminal nodules in question are of fairly general occurrence. a The deductions which he has drawn from the study of this fin appear to m e no less unwarrantable than those of Schneider alluded to above. |
