94 



PISCES 



of the skeletal arch, the efferent being always the innermost next 

 to the arch. 



Since, in each gill-pouch, the branchial lamellae are usually 

 distinctly grouped in an anterior row on the posterior face of one 

 bar, and a posterior row on the anterior face of the next bar (Fig. 

 26), each complete gill is said to consist of two hemibranchs. 



FIG. 57. 



Sections across the gill-arch of A, Mustelus ; B, Ceratodus ; C, Acipenser ; D, Lepidosteus ; 

 E, Salmo ; F, 1'olypterus. a, skeletal arch ; /, afferent artery (black) ; e, septum reaching 

 external surface ; e/, efferent artery (cross hatched) ; g.l, gill-lamellae ; g.r, supporting gill-ray ; 

 r, gill-raker ; s, septum, largest in A, and smallest in E. Anterior lamellae to the right. 



In the reduced first or spiracular gill-slit is present never more 

 than one hemibranch, the anterior or ' mandibular,' borne on the 

 mandibular arch. The hyoid bar may bear a posterior ' hyoidean ' 

 hemibranch ; and the succeeding bars may each have a complete 

 gill (or holobranch). The last bar, embedded in the body-wall, can, 

 of course, never bear more than an anterior hemibranch, and is 



