LUCERNARIDA AND GRAPTOLITDLE. 81 



The digestive cavity of the polypite gives out from its upper 

 extremity a series of radiating gas tro- vascular canals, which 

 proceed toward the margin of the umbrella. These radiating 

 canals are never less than eight in number, and on their way 

 to the margin of the disk they break up into a great number 

 of smaller vessels, which unite with one another to form a 

 complicated net-work. At the margin of the bell they all 



FIG. 24. Generative zooid of one of the Lucernarida (Clirysaora hysoscclla). (After 



Gosse.) 



open into a circular vessel, which in turn sends processes into 

 a series of marginal tentacles, which are often of extraordinary 

 length. Besides the tentacles, the margin of the umbrella is 

 provided with a number of marginal bodies, each of which 

 consists of a little collection of pigment or " eye-speck," and a 

 little sac filled with fluid and containing mineral particles. 

 Each of these marginal bodies is covered and concealed from 

 view by a kind of hood derived from the ectoderm. Hence 

 the name of "hidden-eyed" Medusae applied to these forms, 

 in contradistinction to the " naked-eyed " Medusas, in which 

 the eye-specks are exposed to view. The reproductive organs 

 are usually of some bright color, and " form a conspicuous 

 cross shining through the thickness of the disk." 



