THE LOWER FORMS OF LIFE. 



95 



elastic, but not extensile. But this nectocalyx is distinguished at 

 once from that of the Calycophoridee, by the absence of the loco- 

 motive organ termed the nectocyst. A higher means of locomotion 

 is, however, provided for the Medusae. A fringe round the mouth 

 of the polypite and the margin of the umbrella, as well as the 

 substance of the tentacles, are formed of granular substances, and of 



Fig. 120. Medusa, in profile (the central and opposite parts are easily seen through the 

 bright sparkling substance of the animal) a, the umbrella ; b, the sub-umbrella ; c, poly- 

 pite; d, radiating canals; e, velum (shown by dotted lines); /, marginal canal; </, 

 lithocysts ; h, marginal tentacula ; i, reproductive body ; k, manubrium. 



Fig. 121. a, portion of radiating canals (magnified still more) ; 6, radiating canal ; c, mar- 

 ginal canal ; d, ocelli or lithocysts ; e, tentacles. 



this structure there radiates from the rim and along the sub- 

 umbrella a series of muscular bands, and it is by the contraction of 

 these that the creature moves. Such is the simple structure of these 

 beautiful creatures ; and yet, though simple, mark how we are rising 

 in the scale of being 1 



