254 EVENINGS AT THE MICROSCOPE. 



animal, just below the level of the beautiful flower-like 

 wheels, consists as usual of three sub-globose lobes ; one 

 on each side appropriated to each malleus, and the third 

 descending towards the ventral aspect, which envelops 

 the incus. The mallei are more intimately united to the 

 rami of the incus than in the former type, each uncus 

 forming, with its ramus, a well-defined mass of muscle, 

 inclosing the solid parts, and in form approaching that of 

 a quadrant, or fourth part of a circle ; two flat faces 

 opposing and working on each other. Across the upper 

 surface of the mass the uncus is stretched, as three long 

 parallel fingers arched in their common direction, and im- 

 bedded in the muscular substance ; their points just reach- 

 ing the opposite face of the ramus, and meeting the points 

 of the opposite uncus, when closed. The manubrium is 

 much disguised, by being greatly dilated transversely, 

 forming three bow-like loops of little solidity, to the chord 

 of which the fingers are soldered, not articulated. The 

 surface of the dense muscular mass displays striae, or 

 streaks, parallel to the fingers, and, as it were, continuing 

 their number towards their dorsal extremity, becoming 

 fainter till they are imperceptible. These strias do not 

 disappear wheti the muscular parts are dissolved by potash ; 

 and hence I infer the existence of a delicate investiture of 

 solid substance similar to that of the teeth, &c, inclosing 

 the muscular mass. 



The incus, which cannot be separated from the mallei, 

 thus consists of two portions, corresponding to the rami in 

 Brachionus, &c, each of which forms the lower part of the 

 mass just described. At the ventral extremity they are 

 articulated to a slender fulcrum, which is a little bent 

 downward. The solid framework of each ramus sends off 

 from its inferior surface a slender curved process, which is 

 connected with the extremity of the fulcrum. 



The action of this apparatus is as follows : — The ciliary 

 vortices produced by the waves of the coronal disk, pass 



