88 



MANUAL OF ZOOLOGY. 



1. The 'umbrella ' of the Lucernarida is never furnished with 

 a 'velum,' as is the nectocalyx of the Medusidce. 2. The 

 radiating canals in the former are never less than eight in 

 number, and they send off numerous anastomosing branches, 

 which join to form an intricate network ; whereas in the latter 

 they are not more than four in number, and they do not sub- 

 divide. 3. In the place of the separate and unprotected 

 ' vesicles ' and ' ocelli ' of the Medusidce, the marginal bodies 

 of the Lucernarida consist of these bodies combined together 

 into single organs, which are termed ' lithocysts,' and which 

 are protected externally by a sort of hood. 



The Lucernarida admit of being divided into three orders, 

 viz. : the Lucernariadce, the Pelagidce, and the Bhizostomidce. 

 ORDER I. LUCERNARIAD^:. This order includes those Lucer- 

 narida which have only a single polypite, are fixed by a proximal 

 hydrorhiza, and possess short tentacles on the margin of the um- 

 brella. The reproductive elements ' are 

 developed in the primitive hydrosoma 

 without the intervention of free zooids.' 

 (Greene.) 



In Lucernaria (fig. 21), which may 

 be taken as the type of the order, 

 the body is campanulate or cup- 

 shaped, and is attached proximally 

 at its smaller extremity by a hydro- 

 rhiza, which, however, like that of 

 the Hydra, is not permanently fixed. 

 When detached, the animal is able 

 to swim with tolerable rapidity by 

 means of the alternate contraction 

 and expansion of the umbrella. 

 Around the margin of the umbrella 

 are tufts of short tentacular pro- 

 cesses, and in its centre is a polypite 

 with a quadrangular, four-lobed 

 mouth. ' In transverse section the 

 polypite may be described as some- 

 what quadrilateral, with a sinuous 

 outline, which expands at its four 

 Fig. 21. Lucernaria. lucernaHa angles to form as many deep lon- 



auricula attached to a piece of .. ,. , /> , > .,1 * > i ,-t 



seaweed. (After Johnston.) gltudmal folds, Within which the 



simple generative 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- 



