. The Bashford Dean memorial volume :. Fishes; Sharks; Fishes, Fossil. The Anatomy of Chlamydoselachus 423 surface is very large—perhaps larger, in proportion to body size, than in most elasmo- branchs. The blood vessels of the gills are described in the section on the blood-vascular system, but it may be noted here that, thin as they are, the lamellae nevertheless contain exceedingly rich capillary plexuses. The general plan of a gill of Chlamydoselachus is much like that of Heptanchus (Text' figure 81, which should be compared vv^ith Text'figure 78). Indeed, so far as the gills of elasmobran
. The Bashford Dean memorial volume :. Fishes; Sharks; Fishes, Fossil. The Anatomy of Chlamydoselachus 423 surface is very large—perhaps larger, in proportion to body size, than in most elasmo- branchs. The blood vessels of the gills are described in the section on the blood-vascular system, but it may be noted here that, thin as they are, the lamellae nevertheless contain exceedingly rich capillary plexuses. The general plan of a gill of Chlamydoselachus is much like that of Heptanchus (Text' figure 81, which should be compared vv^ith Text'figure 78). Indeed, so far as the gills of elasmobranchs have been studied, there is a considerable degree of uniformity in their structure throughout the group. From my observations I conclude that the gills of Chlamydoselachus are of the usual elasmobranch type. In proportion to body size, the gill-clefts are unusually long (Text- figure 4); they are separated by very slender branchial arches. The widely-distensible. Text-figure 81. Section, cutting parallel to branchial filaments, through second holobranch of Heptanchus maculatus. ad., adductor muscle; a/., third afferent artery; , branchial ray cut short; csd., fourth dorsal constrictor muscle; eb., epi- branchial segment of cartilaginous branchial arch; , fourth and fifth efferent collector arteries; , extrabranchial cartilage; , anterior filament; , posterior filament; , dorsal interbranchial muscle; n., posterior division of the branchial nerve. After Daniel, 1934, Fig. 143. pharynx is adapted for the rapid expulsion of a large volume of water through the gill- clefts. This, in connection with the large respiratory surface afforded by the gill-filaments and particularly by their lamellae, makes an efficient mechanism for aerating the blood. A discussion of the question as to the phylogenetic significance of the unusually large number of gill-clefts and gill-arches in Chlamydoselachus and the notidanids would lead us too far afield. Consider
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