CCELENTERATA : HYDROZOA. 



I OS 



able rapidity by means of the alternate contraction and expan- 

 sion of the umbrella. Around the margin of the umbrella are 

 tufts of short tentacular processes, and in its centre is a poly- 

 pite with a quadrangular, four-lobed 

 mouth. " In transverse section the 

 polypite tnay be. described as some- 

 what quadrilateral, with a sinuous out- 

 line, which expands at its four angles 

 to form as many deep longitudinal 

 folds, within which the simple genera- 

 tive bands are lodged." — (Greene.) 

 Wide longitudinal canals are formed 

 by septa passing from the walls of the 

 polypite to the inner surface of the cup, 

 and a circular canal runs immediately 

 beneath the insertion of the tentacles. 

 The reproductive elements are pro- 

 duced within the body of Lucernaria 

 itself, without the intervention of any 

 generative zooid. 



Order II. Pelagid^. — This order 

 is defined as including Lucernarida 

 which possess a single polypite only, and 

 an umbrella with marginal tentacles. 

 The reproductive elements " are developed 

 in a free U7nbrella, which either consti- 

 tutes the primitive hydrosoma, or is pro- 

 duced by fission from an attached Liuer- 

 naroid." — (Greene.) 



Two types, therefore, exist in the Felagidte. The one type 

 is represented by a fixed " trophosome," resembling Lucernaria, 

 but distinguished from it by the fact that the generative ele- 

 ments are not developed in the primitive hydrosoma, but in a 

 free "gonosome," which is produced for the purpose. The 

 second type, represented by Pelagia itself, is permanently free, 

 thereby differing from Lucernaria, which it approaches, on the 

 other hand, in the fact that its generative elements are pro- 

 duced in its own umbrella without the intervention of free 

 generative zooids. Pelagia, however, differs considerably in 

 structure from Lucernaria, and in all essential characters is not 

 anatomically separable from a Steganophthalmate Medusid. The 

 process of reproduction as displayed in the first section of the 

 'Felagidce will be considered when treating of that of the Mhi- 

 zostomidcB, there being no important difference between the 

 two, except as concerns the structure of the generative zooids. 



Fig 23. — Lucernariadaa. Z«- 

 certiaria auricula, attached 

 to apiece of sea- weed (after 

 Johnston). 



