. Chimæroid fishes and their development. Fishes; Chimaeridae. DETAILS OF LATER EMBRYO. 107 is long, narrow, and relatively of great size, suggesting its origin from an anterior fin spine, and interesting in connection with paleontological data (^/l figs. 132-137). In fig. 50'', an idea is had of the extent of the overgrowth of the opercular fold on the ventral side of the head, and here is shown also that the external gill-filaments arise onh' from the anterior wall of the gill-slit, and that the external filaments increase in length as they pass toward the middle of each flap. A detail of th
. Chimæroid fishes and their development. Fishes; Chimaeridae. DETAILS OF LATER EMBRYO. 107 is long, narrow, and relatively of great size, suggesting its origin from an anterior fin spine, and interesting in connection with paleontological data (^/l figs. 132-137). In fig. 50'', an idea is had of the extent of the overgrowth of the opercular fold on the ventral side of the head, and here is shown also that the external gill-filaments arise onh' from the anterior wall of the gill-slit, and that the external filaments increase in length as they pass toward the middle of each flap. A detail of the ventral fin is shown in fig. 50*^. Here the mixipterygium is but a further difteren- tiation of the base of the ventral fin ({/. plate viii, fig. 49''), and the anterior clasping organ [ac/) evidently represents the fin's anterior segmental elements (radialia) {cf. also fig. 112). The mouth region in this stage is noteworthy, since it shows that not only are the anterior and posterior dental plates {a(//> and /(T^/) present, but also a series of other eminences which are best interpreted as rudimentary dental plates. Similar structures are now described in detail in the work of Schauinsland on Cal- lorhynchus (v. ni/'ra). The present figure also indicates the early stages in the curious lip cartilages of the Chimaeroid. They arise at the sides of the mouth and suggest at this stage the corresponding structures in shark. In view of the recent work of Schauinsland and of the younger Fiirbringer (Morph. JB., 1903, vol. XXXI, pp. 360-445), we recognize with interest the unpaired element at the mandib- ular symphj'sis which is held to represent the homologue of the basihyal of the hyoid arch. (O! fig. 11 i.) In commenting further upon this stage we note that in the eye the iris is well established, and that in the umbilical sac the \'olk material is arranged in conspicuously concentric lamellae (plate ix, fig. 50''). T/ic Skull.—The skull at this stage may be compared instru
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectfishes, bookyear1906
