THE COD. 103 



the posterior and outer is circular and open, while the 

 anterior and inner is guarded by a flap-like valve. 



87. The large eyes {e), devoid of eyelids and covered 

 with a continuous layer of transparent integument. 



88. The gill- opening, a largfe crescentic aperture on 

 each side, extending from under the throat upwards and 

 backwards along the side of the head ; it is bounded be- 

 hind by the shoulder-girdl-e (§ 95) and in front by the gill- 

 cover or operculum, which is easily distinguishable into two 

 parts, the operculum proper (Fig. 30, op), supported by 

 the opercular bones (§§ 63 — 66), and the branchiostegal 

 membrane {br.m), supported by the branchiostegal rays 

 of the hyoid bone (§ 55). 



8g. 'Ihe gills, seen by lifting up the operculum; they 

 are four in number, and consist of rows of deep red 

 branchial filaments, supported on the four anterior 

 bmnchial arches (§§ 57 — 62) ; between the gills, as well as 

 in front of the first and behind the-'last gill, are the bran- 

 chial cltfts, five in number, leading into the cavity of 

 tlie mouth. 



90. The pseudobranchia (rudimentary hyoidean gill), 

 seen as a red patch covered by semi-transparent mucous 

 membrane, on the inner surface of the gill-cover, a little 

 anterior to the dorsal end of the first branchial arch. 



91. The absence of spiracles (p. 43, § 70) and of external 

 auditory apertures. 



92. The anus (Fig. 30,^), a somewhat prominent aperture, 

 situated in the middle ventral line, about halfway between 

 the snout and the end of the tail. 



93. The genital (g) and urinary {n) apertures, 

 situated on a common elevation of integument, immediately 

 posterior to the anus ; they are small apertures, the genital 

 being the more anterior of the two. 



