DIGESTIVE SYSTEM. 465 



during the process of watching for prey, are highly irritable, and sen- 

 sible of the slightest contact. No sooner does an animalcule impinge 

 upon any part of their surface than the tentacle touched bends with 

 extraordinary quickness, as if endeavouring to strike it towards the 

 mouth ; and if the object be sufficiently large to touch several at the 

 same moment, all the tentacula simultaneously cooperate in seizing and 

 retaining it. 



(1200.) The existence of these cilia upon the tentacula would seem 

 to be characteristic of the Polyzoa, and is invariably accompanied, as 

 far as our information extends at present, with a digestive apparatus of 

 far more complex structure than what we have seen in the unciliated 

 polyps; for in the class before us, besides the stomach, there is a distinct 

 intestinal tube and anal outlet. In the specimen under consideration 

 the organization of the alimentary organs is rendered even more elabo- 

 rate than is usual in the class, by the addition of a gizzard or cavity 

 wherein the food is mechanically bruised before its introduction into the 

 proper stomach. The mouth is placed in the centre of the space en- 

 closed by the tentacula : it appears to be a simple orifice, incapable of 

 much distention, through which the particles of food brought by the 

 ciliary action pass into a capacious oesophagus (fig. 238, a, 1,2); this, 

 gradually contracting its dimensions, ends in a globular muscular organ, 

 to which the name of gizzard has been applied (3). The walls of this 

 viscus are composed of fibres that radiate from two dark points, seen in 

 the figure ; and its lining membrane is covered with a great number of 

 hard horny teeth, so disposed as to represent, under the microscope, a 

 tessellated pavement. The contractions of the gizzard are vigorous; 

 and, from the structure of its interior, its office cannot be doubtful. 



(1201.) To the gizzard succeeds a stomach (fig. 238, a, 4), which is 

 studded with brown specks, apparently of a glandular nature, and 

 probably representing a biliary apparatus. The intestine leaves the 

 stomach at its upper portion, close to the gizzard (5), and, running 

 parallel with the ossophagus towards the tentacula (6), terminates at 

 the side of the mouth (7), in such a position that excrementitious matter 

 is at once whirled away by the ciliary currents. The whole intestinal 

 apparatus floats freely in a visceral cavity that contains a transparent 

 fluid and encloses distinct muscular fasciculi, to be described in another 

 place. 



The process of digestion in this minute yet highly- organized being is 

 well described by Dr. Farre in the memoir above-mentioned. 



(1202.) The little animal, when in vigour, is seen projecting from 

 its cell, with the arms extended and the cilia in full operation, the 

 upper part of the body being frequently turned from side to side over 

 the edge of the cell, the extremity of which, from its peculiar flexibility, 

 moves along with it. The particles carried to the mouth in the vortex 

 produced by the action of the cilia, after remaining a little while in the 



