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 

 imbedded in the muscular substance; their points just 

 reaching the opposite face of the ramus, and meeting the 

 points of the opposite uncus, when closed. The manu- 

 brium is much disguised, by being greatly dilated trans- 

 versely, forming three bow-like loops of little solidity, 

 to the chord of which the fingers are soldered, not arti- 

 culated. The surface of the dense muscular mass disjDlays 

 stria 3 , or streaks, parallel to the fingers, and, as it were, 

 continuing their number towards their dorsal extremity, 

 becoming fainter till they are imperceptible. These stripe 

 do not disappear when 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, ifec, 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 



