DISCOPIIORA ; MEDUSA. 533 



when the whole surface of the ocean, as far as the eye can reach, 

 is seen to exhibit a uniform luminosity, and this is ascertained 

 to be due to animals not larger than the head of a pin, in close 

 apposition to each other, the vast amount of organic life, which 

 ordinarily escapes our notice, can scarcely fail to strike us with 

 astonishment, not unmingled with pleasure at the thought, that 

 each of these little beings is passing a life of enjoyment, and is 

 performing an allotted function in the great oeconomy of Nature. 

 1 186. When we examine one of the larger Medusa (Fig. 723) 

 as it floats in its native element, we find that the central part of 

 the concave side of the disk is occupied by the stomach, in the 



A 



FIG. 723. MEDUSA ; A, under surface, showing the mouth in the centre, surrounded by the tenta- 

 cula, and the ovarial chambers exterior to the origins of these; B, side view, showing the tenta- 

 cula hanging down in their natural position. 



middle of which is the mouth, opening downwards, and sur- 

 rounded by four leaf-like tentacula. Around the stomach are 

 four ovarial chambers, with separate orifices. These organs 

 occupy the space inclosed, as it were, within the frame-work of 

 the umbrella ; but the delicate membranous disk projects con- 

 siderably beyond them, and floats freely in the water. Its 

 margin is often lobed or fringed, and almost always provided 

 with a variable number of slender tentacles, which are usually 

 capable of contracting and elongatii^ themselves to a consider- 

 able extent. The free portion of the disk is traversed by 

 numerous canals, which arise either from the stomach itself or 

 from a cavity situated immediately above that organ. Eight of 

 these pass directly outwards, and terminate in a circular canal 

 which runs round the edge of the disk, and in this eight small 

 orifices are observed, serving for the discharge of foecal matter. 



