343 



contiuuous line of pores, likę the lateral liue of fish and Trituns, 

 vvhich is continued on the tail some distance beliind the base of the 

 hinder members, but becoming less distinct at the hinder part of 

 the series. 



The eyes are of modeiate size, scarcely raised above the surface, 

 round, without any eyehds ; the pupil is black, small, circular, less 

 than one-third the diameter of the globė, with a narrow golden iris. 

 The Mud Fish is generally to be observed swimming about uuder 

 the water, or resting at the bottom of the tank, supporting itself by 

 its members, an inch and a half or two inches above the surface 

 of the gravel, with its nose generally in the corner, bent down and 

 partly hidden in the gravel. 



The mouth is firmly closed by the overhauging upper lip, except 

 in front, where there is a small oblong, transverse, horizontai open- 

 ing on the outer edge of the lips, admitting the water to the small 

 open external nostrils, which are on the middle of the under side of 

 the upper lip. This opening does not extend to the hinder part of 

 the lips, which are closed behind it, so that water cannot enter the 

 mouth in that direction except through the nostrils. 



In this quiescent statė the lateral gill-opening is generally closed, 

 but sometirnes it is slightly elevated, and a small current appears to 

 be emitted now and then from it, as if a small ąuantity of water were 

 taken in by the nostrils and emitted by the gill-flap ; but this action 

 is not coutinuous nor very distinctly visible. 



While remaining uuder the water the animal sometirnes opens the 

 mouth to its full extent, leaving it open for some time, dilating the 

 throat by the action of the os hyoides ; when fuUy dilated it closes 

 its mouth, opens the gill-aperture, and contracting the throat emits 

 a strong current of water through the lateral gill-aperture. 



It occasionally but at uncertain periods rises perpendicularly to the 

 top of the water, until the front part of the head and the whole 

 mouth are exposed above the water ; it then opens its mouth, which 

 it retains open for a time, dilates its throat, as if taking in all the air 

 it can contain, closes the mouth, descends under the surface and con- 

 tracts its throat, as if it were foroing the air into the lungs (sometirnes 

 during this action one or two very small bubbles of air are emitted at 

 the gill-aperture), and then the animal takes up its old position near 

 the bottom of the vase. 



I once saw the animal asceud and so take in air almost imme- 

 diately after it had been passing a fresh supply of water to its gills, 

 When I have been observing it, it appeared to take in air more fre- 

 quently than water *. It often rises with its body perpeudicular, as 



* Mr. W. Hawkin8 in the ' Illustrated News ' observes : — " It is seeu habitually 

 to rise to the surface of the vvater for a larger supply of atmospheric air, thrusting 

 its open mouth above the surface." 



Dr. Holbrook appears to have observed the šame habit in the Necturus macu- 

 loms (whicli is probably the lar\a of the Hell-bender or Protonopsis horridd). 

 He States that that animal in confinemeiit " asceuds to the surface (of the water), 

 taking in a raouthful of air, and sinks again with it to the bottom." — Amer. 

 Herpet. i. 113. 



