WHEEL-BEAREBS. 255 



together through the upper sinus, and are hurled in one 

 stream along the centre of the face, nearly to the project- 

 ing chin. Here is placed the orifice of the buccal funnel, 

 a perpendicularly descending tube of considerable width, 

 slightly funnel-shaped at the top, the interior surface of 

 which is strongly ciliated. It descends straight upon the 

 mastax, over the part where the unci unite. But just 

 above this point there are two valves projecting from the 

 walls of the tube, also well ciliated. These can be brought 

 into contact, or separated in various degrees, at will ; and, 

 being very sensitive, they regulate the force of the inflow- 

 ing current, and doubtless exclude hurtful or useless sub- 

 stances. The current now flows along the two rami of the 

 incus, as I have already described ; and, passing between 

 their separated points, descends into the oesophagus, a 

 slender duct opening beneath them, and leading to the 

 digesting stomach. 



As this current passes, the manducatory apparatus acts 

 upon the particles of food which it brings in its course. 

 The quadrant- shaped masses approach each other and 

 recede, with a rapid rolling movement, in the direction of 

 the curvature of the mallei ; while, at the same time, the 

 rami of the incus open and close their points, rise and 

 sink, and occasionally perform a kind of shovelling action. 

 The points of the fingers of the unci, meeting each other, 

 doubtless pierce and tear the Infusoria swallowed, and the 

 striated faces bruise, squeeze, and grind them down. 



When the muscular investment is dissolved away by 

 potash, the essential identity of the whole structure with 

 that of the type already described becomes abundantly 

 evident. Even the mallei, which in some aspects present 

 difficulty, when viewed vertically, are but little changed ; 

 the fingers are parallel instead of divergent, and the handle- 

 like character of the manubrium is lost ; but three areas, 

 inclosed by loops or carinae of solid substance, reveal their 

 true nature. 



