in the Fcetus of Vertebrated Animals. 107 



alluded to best known, appear to be all truly aquatic in their 

 habits, or to live chiefly in water and moist mud ; but all of 

 them are provided with organs analogous to the lungs of the 

 adult batrachia, and appear to respire more or less air as well as 

 water. 



The principal respiratory organ of the Proteus and Siren is' 

 the external gills, into which a large quantity of the blood of 

 these animals is propelled ; while the Amphiumas (at least the 

 adult animals) appear to be altogether destitute of gills, and to 

 respire, like the batrachia after they have undergone the trans- 

 formation, by lungs alone, into which air is from time to time 

 introduced. 



Rusconi, in his beautiful Memoir on the Proteus anguinus, 

 states, that this animal dies as soon as or sooner than most fishes, 

 when taken out of the water. Mr Neill has observed, that the 

 siren which he possesses lived, upon one occasion, for twelve or 

 fourteen hours out of water, and Cuvier informs us, that the 

 Amphiumas or Abranchi are known frequently to lie in dry 

 places for several days, without sustaining any injury ; on the 

 other hand, the whole of these animals, even the abranchous 

 amphiuma, appear capable of remaining below water for a con- 

 siderable period, without inhaling air, which the existence of 

 lungs in them would lead us to believe is necessary for their 

 respiration. 



The external gills of the proteus and siren are fimbriated and 

 branched like those of the salamander; and the principal stalks are 

 suspended, in the same manner, from branchial plates or hoops, 

 which appear to be processes of the hyoid bone. There are also 

 three apertures between these branchial hoops, through which 

 these animals are enabled to expel either air or water, and thus 

 produce currents near the gills. 



Though the amphiumas are destitute of any kind of gills, it is 

 a very curious and interesting fact which has been established by 

 Cuvier, that the hyoid bone in these animals bears a consider- 

 able resemblance to that of the siren, and other animals in which 

 external gills exist, either permanently or for some period of 

 their life. The hyoid bone consists, in the amphiumas, of a 

 lingual part and two long comua, which encompass the pha- 

 rynx. Near the two posterior extremities of these comua, ther© 



