SUB-CLASSES LUCEliNARIDA, ORAPTOLITID.'E, ETC. 79 



series of marginal tentacles, wbicli 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 col- 

 lection of pigment, or "eye-speck," and a little sac filled with fluid 

 and containing mineral particles. Each of these margiiial bodies 

 is covered and concealed from view by a kind of liood derived from 

 the ectoderm. Hence the name of " hidden-eyed " Medusce, applied 



Fig. 4.'i. — G(;iier;tM\e zmiiil nf one of tlie Lurernarula (ChrySfinni hy f:rrlJ<i). 

 (After Gosse.) 



to these forms, in contradistinction to the " naked-eyed " Jfcdusa; 

 in which the eye-specks are exposed to view. There is also a well- 

 developed nerve-ring running round the mouth of the umbrella. The 

 reproductive organs are usually of some Ijriglit colour, and "foini a 

 conspicuous cro.ss shining through the thickness of the disc." 



From tlie aljove description it will Ije eviiU-nt tli;it llnre is a eoiisideralilL' 

 resemblance between the so-called " hiilden-eyed" ./V/6(//^A'tr, or the reiu-oduc- 

 tive zooids of many of the Lucernarida, and the ]iiednsiforni gonopljores of so 

 niany of the Hydrozoa, as well as the true Mcdnsidtr ur naked-eyeil Nedusce. 

 The differences, however, lietween them are these: The swininiing-disc of the 

 naked-eyed MeUvsce and of auy medusiforni gonophore is furnished at its mouth 

 with an internal shelf or veil ; the radiating gastro-vasenlar canals are very 

 rarely more th;in four in immlicr. and ^;ho^ld they subdivide (as in rare cases 



