344 



if it were going to take in free air, but descends agaiu without reaching 

 the surface of the water. 



The organs of respiration of this animal are twofold : — 



1 . Well-organized gills on the inner edge of the branchial arches, 

 as in fishes, and a regular gill-cover with a small oblong aperture ia 

 front of the base of the anterior members (see Owen, Trans. Linn. 

 Soc. xviii. t. 25. f. 3, t. 26. f. 1). 



2. Two well-developed cellular lungs of nearly equal size (see 

 Owen, Trans. Linn. Soc. xviii. t. 25. f. 3, t. 26. f. 1, 2). 



3. The uostrils are olose together, situated on the under side of 

 the inner lip, with their internal opening on the side of the mouth 

 between the hps and the outer edge of the large inner series of teeth ; 

 the passage is short, as a probe is easily passed from the one open- 

 ing to the other, and the inner nostrils are very evident in the Uving 

 animal when it opens its mouth to take in air. 



M. Bischoff observed these interior nostrils also in the Curamuru 

 or Lepidosiren paradoxa of the Brazils. 



The animal is, therefore, provided with well-deTeloped organs for 

 both aerial and aquatic respiration, and its manner of breathing is 

 perfectly conformable to this organization : it is conseąuently the 

 most perfectly amphibious animal, equally adapted for living on land 

 or in water, that has come under my observation. 



The character which best separates the Batrachian — as the Toad, 

 Frog and Salamander — from the Fish, is, that in both the larva and 

 perfect statė they are provided with an external and internal nostril, 

 and it is through this nostril that these animals take in or emit the 

 air which they respire ; while in fish, the water which they respire 

 is taken in by the mouth, and after passiug over the gills is emitted 

 by the lateral aperture of the gill-flap ; the nostril being only a sac, 

 without any communication with the cavity of the mouth. 



When a Batrachian respires, the mouth is kept closed, the throat 

 being used likę a pair of bellows to force the air into the lungs ; and 

 if the mouth is kept open, the animal dies for want of the power 

 of respiring. In fish, on the contrary, the mouth is always more 

 or less open, the fish either constantly gulping in the water, then 

 closing the mouth or lips, and emitting it by the lateral opening ; 

 or the mouth is partially open, and the animal uses its tongue 

 and the hinder internal edge of the lip as a kind of yalre, by which 

 the cavity of the mouth is closed and the water is forced to pass 

 through the gills. 



The Lepidosirens appear to take in Avater by the nostrils, and at 

 the šame time to respire both air as Batrachians and water as fish. 



The generality of the Amphibia, as the Toads, Frogs, and Efts or 

 Salamanders, are organized for aąuatic respiration in their young and 

 lower statė, and for aerial respiration in their adult condition ; but 

 this animal has both kinds of organs in a statė fit for perfect use at 

 the šame time, and the animal evidently uses them simultaneously. 



It appears to me that the Mud-fish is much more nearly related 

 to the Amphibia than to any fish that I am acquainted with ; at the 

 šame time it evidently forms a particular group in that class. 



