256 CHARACTERS OF VERTEBRATE ANIMALS 



vertebrae exhibit the primitive feature of biconcave centra, and 

 small movable ribs are attached to them. There is no sternum, 

 and even the limb-girdles are absent. As in Snakes, some of 

 the internal organs are modified to suit the narrow shape of the 

 body, and it may be mentioned in particular that the right lung 

 is much larger than the left. In regard to the sense organs, it 

 may be noticed that the small eyes are hidden under the skin 

 and the sound-conducting middle ear is absent. The develop- 

 ment of an East Indian form (Epicrium glutinosum) has been 

 studied, and presents some curious points. When the embryo 

 is hatched it possesses three pair of external gills, a pair of gill- 

 slits, a short tail, and traces of hind-limbs. Immediately hatching 

 takes place, however, these gills are lost; but in spite of this the 

 larva takes to the water and lives there for some time. 



