136 CLASS MAMMALIA. 



Although there is, at the entrance of the sac, a sphincter 

 which is very apparent, yet it is not by means of it, or at 

 least by means of it alone, that the return of the air is re- 

 sisted. There are large valvulae on the neck and back, 

 which are charged with it. 



The air proceeding from the sphincter, takes the front 

 of the ear in its way, passes into the sinus of the forehead, 

 from whence it reaches the vertex, the occiput, and the 

 upper part of the neck. It is there that it is discharged 

 into the great sac. 



Thus, the nyctere manages exactly like the tetrodons, 

 ( Tetraodon lineatus, L.) It carries, at pleasure, a mouth- 

 ful of air in its sac, then a second, and so on. It breathes 

 exactly as we ourselves can do, in the very same manner, 

 in fact, that we do breathe, with this difference only, that 

 it breathes into its mouth, the cavity of which, is then 

 without any external passage. It then becomes a true blad- 

 der, within which, the trunk is, as it were, deposited. 

 Thus inflated, it assumes a spherical form, and in this state, 

 the animal bears no indistinct resemblance to a balloon, to 

 which wings, a head and feet have been attached. 



More fortunate than the tetrodon, which cannot have re- 

 course to a similar operation, without reducing itself to an 

 inert mass on the face of the waters, the nyctere preserves 

 all its faculties, or to speak more truly, it augments their 

 energy, by becoming more light, and more capable of velo- 

 city, in the act of flying. 



It was natural to suppose that such singular anomalies 

 in the olfactory conduits, would influence another system of 

 organs, and perhaps occasion considerable changes else- 

 where. We find, in fact, that this extensive sac modifies, 

 or rather procures for the nycteres, a most valuable ap- 

 pendage to the respiratory organ. If this same apparatus, 

 which is so well adapted to their system, be not, in truth, the 

 motive of those modifications of the nasal cavities, and will 



