SEA-FISHERIES LABORATORY. 151 



opened, it will be seen that the whole jaw apparatus 

 swerves towards the eyeless side. The mechanism by 

 which this is effected is described elsewhere. The expla- 

 nation of this asymmetry is that the fish must seek its 

 food on the sea bottom, and the torsion of the jaws towards 

 the under side is hence a physiological convenience, if 

 not a necessity. The same consideration explains why the 

 teeth, which are blunt and flattened, and not pointed like 

 those of the cod, are situated almost entirely on the eyeless 

 side. Within the mouth will be seen the maxillary and 

 mandibular breathing valves, or " internal lips/' to pre- 

 vent the regurgitation of water through the mouth on the 

 fall of the gill cover. f The anus is situated very far 

 forward in front of the " anal spine," and is a large 

 median opening elongated from before backwards. The 

 urinary papilla of the female is distinctly on the ocular 

 side, a little distance above and behind the anus. The 

 oviducal aperture is large and lies immediately behind the 

 anus. It is very obvious in the spawning season, but at 

 other times of the year we have failed to find it, so that 

 it is either occluded then, or very minute. In the imma- 

 ture fish we believe it does not exist. In the male the 

 papilla is in the same position, but is here a urinogenital 

 papilla. We have failed to find any external distinction 

 between the two sexes, but the male is smaller than the 

 female when it first becomes mature. The pair of anterior 

 and posterior nostrils on each side are on the ocular side 

 situated between and in front of the two eyes, and on the 

 eyeless side in front and to the left of the left eye. 



Between the two eyes and passing backwards there is 

 a prominent ridge formed almost entirely by the right 

 frontal, and in a line continued back from this ridge are 



tDahlgren, Zool. Bui]., 1898. 



