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 2.5 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 specimens of the adult Chlamydoselachus do have such a semblance. Allis 

 (1923) has a drawing (reproduced by Gudger and Smith, 1933, in their Fig. 7, pi- II — 

 Article V of this Memorial Volume) made from an adult head supplied to him by Dean, 

 which shows such remnants of protruding filaments as are seen in Dean's figures on 



