122 



HYDROZOA. 



and, externally, by the cup itself. The outer 

 canals are closed superiorly by a roof, consisting 

 of four inflected lobes from the summit of the 

 cup ; the inner spaces remaining open. There are 

 also four very narrow canals coinciding with the 

 lines where the vertical septa and inner surface of 

 the cup meet ; and formed, it would seem, partly 

 by these septa and partly by folds in the cup's 

 substance. Lastly a circular sinus has its course 

 immediately beneath the insertion of the ten- 

 tacles. 



Fig. 25. 



LucEBNABiA : — Two specimens of Lucernaria auricula, attaclied 

 to a piece of sea-weed. That figured to the right is somewhat 

 abnormal, haying a ninth tuft of marginal tentacles. (Natural 

 size.) 



By means of a band of muscular tissue which 

 traverses its margin, and another set of fibres 

 which radiate towards the polypite, the distal ex- 

 tremity of the cup can fold inwards and contract 

 itself at the pleasure of the animal. Some Lucer- 

 nariadce have been observed to detach themselves, 

 and swim in an inverted position by the slowly 

 repeated movements of their cup-like umbrella. 

 In this respect they agree with Pelagia, a much 

 more active and permanently free member of the 

 same order. 



