133 



MANUAL OF ZOOLOGY. 



which, however, like that of the Hydra, is not permanently 

 fixed. When detached, the animal is able to swim with toler- 

 able rapidity by means of the alternate Contraction and expan- 

 sion of the umbrella. Around the mar- 

 gin of the umbrella are tufts of short 

 tentacular processes, and in its centre 

 is a polypite with a quadrangular four- 

 lobed mouth. " In transverse section 

 the polypite maybe 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 be- 

 neath 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^E. This order 

 is defined as including Lucernarida 

 which possess a single polypite only, and 

 auricula attached an umbrella with marginal tentacles. 

 joh a ns p ton c ) e . fsea - weed(after The reproductive elements "are'devek 

 oped in a free umbrella, which either con-^ 



stitutes the primitive hydrosoma, or is produced by fission from an 

 attached Lucernaroid " (Greene). 



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

 is represented by a fixed " trophosome," resembling Luceri 

 naria,\)\& distinguished from it by the fact that the generative 

 elements 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 gen- 

 erative zooids. Pelagia, however, differs considerably in struc- 

 ture 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 Pelagida will be considered when treating of that of the 



Fig- 57- Lucernariadae. Lu- 



