226 HIGHWATER MARK. 



of each cell there is seated, at the point where it 

 springs from the summit of its predecessor, a kind of 

 oval knob, which is cleft to receive, as in a socket, a 

 more slender shelly knob. To this is attached, by a 

 very free hinge-joint, a long and very slender horny 

 bristle, tapering to a fine attenuated point. The 

 course of this lash is so curved, that it passes across 

 the front of its own cell. Its movements are curious : 

 ever and anon, fitfully and suddenly, it is swept for- 

 cibly along from one end of its range to the other. 

 It is believed that its use is to brush away any ex- 

 traneous matters that, lodging upon the cell, might 

 interfere with the comfort of the inhabitant; or minute 

 intruders whose presence is felt to be annoying ; or to 

 give a hint to larger visitors that their room is better 

 appreciated than their company. This conclusion is 

 strengthened from the circumstance that the range 

 covered by the vibraculum in its sweep, includes the 

 area of the aperture, where violence and annoyance 

 are more liable to be felt than in other parts. 



Much more curious, however, than either operculum 

 or vibraculum, is the avicularium, or bird's-head. 

 The outer angle of the summit of each cell carries 

 what at first sight you would perhaps take for a stout 

 triangular knob ; but when you look at it more care- 

 fully, you see that it is a very special and singular 

 organ. It is like the stout and strongly-hooked beak 

 of some strange bird of prey, cut out of its skull, and 

 soldered, upside down, to the angle of the cell. The 

 upper mandible (or what, in the true bird's beak, 



