26 



THE ELASMOBRANCH FISHES 



INTEGUMENT OF ELASMOBRANCHS IN GENERAL 



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The description given for the layers of the integument in Heptanchus may 

 serve to portray conditions which are more or less general. There is, however, 

 in the different Elasmobranchs considerable variation in the thickness of the 

 integument, affecting one or both of the layers. In a type like Scymnus, for 

 example, the upper or epidermal layer is thinner than that of Heptanchus, 

 yet the corium of Heptanchus is relatively thin, so that its integument as a 



whole is of medium thickness. The 

 thickening of the skin may be due 

 to the addition of many cells to the 

 corium as, for example, in Het- 

 erodontus, or it may be brought 

 about as in Triakis ( fig. 29 ) , where 

 the dermal cells, particularly in 

 the superficial layer, are much 

 less compact. 



Color in the Elasmobranchs 

 while varying considerably usu- 

 ally assumes a quiet hue, the bril- 

 liant reds or blues characteristic 

 of the bony fishes rarely being 

 present. The color may be a light 

 drab as in Mustelus calif ornicus, 

 a deep blue as in the lamnoids, 

 brown as in Torpedo {Tetronarce 

 calif ornicus), or black as in Tor- 

 pedo occidentalis. It may be scat- 

 tered over dorsum and venter 

 alike as in the deep-sea forms, 

 Spinax of the Mediterranean and Etmopterus of Formosan waters; or it may 

 be confined largely to the dorsum as in Oaleus, Acanthias, and a host of other 

 types; again, it may be collected in a remarkable pattern over a drab back- 

 ground as is characteristic of Cheiloscyllium and the Leopard shark, of Tigri- 

 num and Rhinodon typicus. Whether the color be light or dark or variegated 

 it is produced by chromatophores, several types of which are present. 



The melanophore containing black or brown melanin is usually considered 

 to be a connective tissue type of celP rhizopod in shape, and sometimes capable 

 of amoeboid movement. Some of these cells in Heterodontus (pg., fig. 30) 

 though typically rhizopod are capable of but slight change of form. Other 

 melanophores, smaller in size, may have numerous processes which in extreme 



1 There is evidence for the belief, however, that this cell is derived from a smooth 

 muscle cell. 



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Fig. 29. Section of the integument of the 

 Leopard shark, Triakis semifasciatus. 



b.m., basal membrane ; d.p., dermal papilla ; 

 €.0., enamel organ; g.c, goblet or gland cell; 

 gr., basal or germinative layer of epidermis; 

 ll.c, lateral line canal; n., ramulus of vagus 

 nerve; pg., pigment; s.c, sensory column. 



