OCR Text |
Show is no such cavity. The swim-bladder diverticulum in Hyodon and Notopterus is of an entirely different character. It is large in size, its outer wall is of fibrous tissue, and its inner wall is constituted by the exoccipital and basioccipital in the former, and the opisthotic and basioccipital in the latter genus. The want of uniformity in the relations of the air-vesicles in the above-mentioned fishes, coupled with the occurrence of such vesicles in Mormyroids, in which the relations are yet again different, points to the conclusion that such adaptive features cannot be relied upon to any large extent in determining whether any two fishes are closely or distantly related. The opisthotic or intercalary bone does not appear to be at all constant in bony fishes, as has already been pointed out by Vrolik (Niecl. Arch. f. Zool. i. 3, 1873), Klein (Jahresh. Ver. vaterl. Naturk. Wiirtt. xxxv. 1879), and Sagemehl (Morphl. Jahrb. ix. 2, 1883). It must here be borne in mind, however, that what Gill calls the opisthotic is not the bone that is now generally known as the opisthotic, but the squamosal, which is of invariable occurrence. (See Proc. U.S. Nat. Mus. xiii. 1890 (1891), pi. 30. figs. 2-4, and pi. 31. figs. 2, 4, & 5.) In this matter he appears to be following the now obsolete terminology of Huxley (see Gunther, ‘ Study of Fishes,' 1880, p. 60). Except in the Gadoid fishes, the opisthotic is never of very large size. It is well developed in Hyodon and Megalops, and is moderately large in Notopterus, Gonorhynchus, Osteoglossum, Arapaima, and Heterotis ; in most of the Clupeidse it is small; it is absent in Engraulis and Coilia, in the Mormyridse and in Alepocephalus. As a general rule, in the forms under consideration, the lateral wing of the parasphenoid that passes up along the anterior edge of the pro-otic is of very small extent. In Osteoglossum leichardti, however, it rises so high as to meet the alisphenoid, and in Osteoglossum bicirrhosum, Osteoglossum formosum, and in Gonorhynchus it enters into relation with both alisphenoid and postfrontal. This is not exactly comparable with what occurs in Amia, for in that genus there is one long process of the parasphenoid to the endosteal postfrontal (sphenotic), and a separate shorter one to the alisphenoid. It may here be noted that Swinnerton (Quart. Journ. Micro. Sci. xlv. 4, 1902, p. 532), in mentioning the union of processes of the parasphenoid and frontal immediately in front of the postfrontal bone in Gastrosteus, quotes Klein as having recorded a similar relation obtaining in the case of Lophius. The junction, however, in Lophius occurs in front of the optic foramen, and is in no way comparable with the above. Although the view of Leydig (Zeitschr. f. wiss. Zool. v. 1854), Hertwig (Arch. f. mikr. Anat. xi., Suppl. 1874; also Morph. Jahrb. "ii. 1876), Sagemehl (Morph. Jahrb. ix. 2, 1883), and Klaatsch (Morph. Jahrb. xxi. 2, 1894), that such bones as the vomer and parasphenoid have arisen by the coalescence of tooth-bases, is not shared by Walther (Jen. Zeitschr. xvi. 1882) and Carlsson (Zool. Jahrb. viii. 2, 1894), who claim that tooth-bearing 1 9 0 4 . ] OSTEOLOGY OF THE ELOPID.E AND ALBULIDjE. G3 |