. The Bashford Dean memorial volume :. Fishes; Sharks; Fishes, Fossil. The Embryology of Chlamydoselachus 629. Text-figure 33 A drawing of a 28-mm. Squalus acanthias in about the same stage of external gill-filament develop- ment as is the young Chlamydoselachus shown in Text-figure 32. After Scammon, 1911, Fig. 30a, PI. III. frilled shark could be straightened out they might be as long as those of the dogfish. The two little sharks are shown in the same size, though in life Chlamydoselachus is times longer than Squalus. This shows how much faster and farther the dogfish had gone in develo
. The Bashford Dean memorial volume :. Fishes; Sharks; Fishes, Fossil. The Embryology of Chlamydoselachus 629. Text-figure 33 A drawing of a 28-mm. Squalus acanthias in about the same stage of external gill-filament develop- ment as is the young Chlamydoselachus shown in Text-figure 32. After Scammon, 1911, Fig. 30a, PI. III. frilled shark could be straightened out they might be as long as those of the dogfish. The two little sharks are shown in the same size, though in life Chlamydoselachus is times longer than Squalus. This shows how much faster and farther the dogfish had gone in development. For a frilled shark of approximately the same size as this Squalus, see Figure 23, plate II of a 34'mm. Chlamydoselachus. In Dean's figures of older embryos measuring 124, 175, 185, 240, and 390 mm., and all drawn at an earlier date then those of 46, 54, 66, and 103 mm., the external filaments are very much reduced. They are hardly visible underneath the flaps. From all the data carefully marshalled above, I draw the conclusion that these so-called external gills of the larval frilled shark are nothing but precociously overgrown permanent gills, which later on shorten until but a bare remnant shows beyond the gill-opening, as may be seen in the largest (390-mm.) embryo portrayed by Dean (Figure 49, plate V). From these facts, found in the drawings cited, it is clear that these protruding gill- filaments in the embryos of Chlamydoselachus are not true external filaments like those of the Crossopterygii, Dipnoi, and Amphibia. In the larvae of the dogfish and of the various rays dissected and studied by me, the external filaments are many, long, and plu- mose. By the time of hatching these have disappeared. Whatever may be the part of these external gills in the nutrition and respiration of the embryo, they are almost always absent in the adult. EXTERNAL GILL-FILAMENTS IN THE ADULTS No other adult shark or ray known to me has even the semblance of external gills, but some s
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