I04 MANUAL OF ZOOLOGY. 



CHAPTER XL 



LUCERNARIDA AND GRAPTOLITIDJE. 



Sub-class IV. Lucernarida {Acalephcz, in part). — The mem- 

 bers of this sub-class may be defined as Hydrozoa "whose hy- 

 drosotna has its base developed into an ' umbrella,' in the walls oj 

 which the reproductive organs are produced." — (Greene.) 



A large number of forms included in the Lucernarida were 

 described by Edward Forbes under the name of Steganopbthal- 

 mate Medusa, being in many external characters closely similar 

 to the MedusidcE. These " hidden-eyed " Medusce are familiar 

 to every one as "sea-blubbers" or "sea-jellies," and they 

 occur in great numbers round our coasts during the summer 

 months. The resemblance to the little jelly-fishes is especially 

 strong between the disc or " nectocalyx " of the true Medusidce 

 and the " umbrella " of the Lucernarida, the latter being often 

 • a bell-shaped swimming organ, with marginal tentacles, and 

 containing one or more polypites. These analogous structures 

 (figs. 2 2 and 25) are, however, distinguished as follows J^— 

 I. The "umbrella" of the Lucernarida is never furnished with 

 a " velum," as is the nectocalyx of the Medusida. 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 rarely more than four in number, and though they 

 may subdivide, they do not anastomose. 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 Rhizostomidce. 



Order I. LucernariaD/E. — 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 zoSids.'' — (Greene.) 



In Lucernaria (fig. 23), 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 hydrorhiza, 

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

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



