420 



state of repose, attempting to seize the fish, which they never 

 succeeded in doing. In about ten days the menobranchs had 

 nothing left of the gills but the almost bare cartilaginous sup- 

 ports, with only here and there a branchial fringe. The fish 

 were then taken out, and the branchial fringes began to grow 

 again, and in the course of six months had regained about half 

 their normal size. He had watched these reptiles for two sum- 

 mers, and no similar falling of the gills ever took place, so that it 

 appears in the present instance that the fish actually eat them off, 

 their loss being a pathological and not a natural phenomenon — 

 in either case this fact seems interesting in a physiological point 

 of view, as bearing upon the respiratory organs of these reptiles. 

 He had ascertained (see page 153 of this volume) experimentally 

 that they survive out of water about four hours, showing that 

 their pulmonary sacs, or lungs, are not alone sufficient for the 

 maintenance of respiration. In the present instance, though their 

 pulmonary sacs were the principal respiratory organs, the animals 

 did not apparently suffer. These lungs are two, one on each 

 side, cylindrical, with thin transpai'ent walls like the air-bladder 

 of fishes, with vessels ramifying through their thickness ; they 

 open anteriorly by a common trachea into the oesophagus, and are 

 about two inches long and one sixth of an inch in diameter. 

 According to Dr. Gibbes, the branchiae are supplied with blood 

 by the branchial artery coming directly from the ventricle, while 

 no branch of this artery runs to the lungs, which are supplied 

 from the aorta. These animals, even when their bi-anchia3 are in 

 full play, occasionally come to the surface and swallow air, which 

 they emit in the water with a faint squeak, by means of the vol- 

 untary muscles with which the lungs are supplied. 



The question arises, why are these lungs apparently sufficient 

 for respiration in the water, and not in the air, though the respired 

 element be in both cases the same ? As there is no evidence of 

 internal gills, the reason must be, that in the air, while the 

 branchial tufts, from dryness are unfit for circulating the blood, 

 the complementary respiration of the skin, so importiint in rep- 

 tiles, cannot be carried on — the pulmonary sacs alone are in- 

 sufficient for the aeration of the blood, and the animal dies. In the 

 water, however, though the branchiae, as in this case, be useless, 

 the cutaneous respiration is unimpeded, and with the pulmonary 



