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Bashford Dean Memorial Volume 



transverse secondary folds or lamellae (Text-figures 78, 79, 80 Im.) too small for ordinary- 

 observation. Goodrich (1930) and some others apply the term lamella to the structure 

 that I have called a filament, and designate as ''secondary lamellae" the small leaf-like 

 folds that I have called simply lamellae. In my specimens, the distal end of a gill-filament 

 is free for a distance of from 3 to 8 mm. ; the gill-filaments never reach the distal edge of 

 the septum, but leave a smooth outer portion (from one-fourth to one-half of the entire 

 surface of the septum) constituting the gill-flap or gill-fold. Successive gill-flaps overlap 

 like the shingles on a roof. In addition to affording protection to the delicate gills, 

 they function as respiratory valves. 



Text-figure 79. Text-figure 80. 



Sections showing filaments and lamellae of 

 a gill of Chlamydoselachus. 



Text-figure 79. Portion of a section (x 12) 

 through the ventral part of the gill of the 

 fourth arch on the right side, cut trans- 

 versely to the filaments. 



a.hr., afferent branchial arteriole; e.hr., efferent branchial 



arteriole. 



Drawn from a section of a giU from a specimen lent by 



Dr. E. Grace White. 



Text-figure 80. Outline of a portion of 

 a section (x 36) taken lengthwise of a gill- 

 filament, in the ventral part of the gill of 

 the first arch on the right side. The upper 

 end of the figure is distal. 

 a., arteriole; \m., lamella. 

 Drawn from a specimen in the American Museum of 

 Natural History. 



All the gill-filaments between two successive gill-clefts, together with the structures 

 supporting these gill-filaments, constitute a holobranch or entire gill. One of these is 

 shown, in a radial section cutting lengthwise of the filaments, in Text-figure 78. The 

 filaments on one side of a gill-septum constitute a demibranch or half-gill. There is 

 a demibranch on both sides of each gill-cleft of Chlamydoselachus, excepting the posterior 

 side of the sixth or last gill-sHt. In my specimens, as in Carman's figure, the filaments on 

 the anterior side of a gill-cleft are always longer than those on the posterior side. In 

 other words, the filaments of a posterior demibranch (posterior with reference to the 

 septum, not to the gill-cleft) are always longer than those of the anterior demibranch of the 

 same giU. Further, the filaments on both sides of the first gill-cleft are distinctly shorter 

 than those in corresponding positions with reference to the other gill-clefts. Since the 

 close-set filaments, all bearing numerous lamellae, of each demibranch are distributed 

 along the entire length of each gill and extend, on the average, considerably more than 

 halfway from the base of the septum to its free edge, it is apparent that the respiratory 



