CLASSIFICATION OF CCELENTERA. 



155 



The complex structure of the Acraspeda, or true jelly fishes, together 

 with the special points already noticed, seems, however, to justify their 

 association with the sea anemones rather than with the simpler Craspedote 

 forms. The classes are then arranged thus : — 



A. Class Hydrozoa, 



B. Class Scyphozoa. 



{Hydrophora. 

 Hydrocorallinre. 

 Trachymedusa?. 

 (^ Order 2. Siphonophoris. 



1' Lucernarice. 

 Sub-class I. Scyphome- | Discomedusa;. 

 dusce, or Acraspeda. 1 ConomedusK. 

 (.Peromedusse. 



Sub-class 2. Anthozoa, ) 

 or Actinozoa. 



C. Class Ctenophora. 



Order (I). 



Zoantharia. 

 Order (2). 



Alcyonaria. 

 [Rugosa.] 



A. Class Hydrozoa. 



There are two types, polypoid and medusoid, which may be combined 

 in one life history. The mouth leads directly into the gastric cavity. 

 The mesoglcea is simple, and \vithout migrant cells. The reproductive 

 cells seem to be usually ectodermic. 



I. Order Hydromedusae. — Simple or colonial forms in which the 

 se.Kually reproductive persons are either liberated as free swimming 

 medusoids, or are sessile gonophores. 



{a) Ilydrophora. — Two types are included here. The first includes 

 the Tubularians, Hydractinia, and other forms in which the polypes are 

 not enclosed in the protective sheath which often surrounds the colony 

 (gymnoblastic), and in which the free medusoid forms, when present, 

 have their genital organs placed in the wall of the manubrium (Antho- 

 medusae), and are furnished with ocelli placed at the base of the 

 tentacles. Hydra and its allies may be included here. 



E.xamples : — 



Syncoryne sarsii, the free medusoid of w^hich is called Sarsia 

 ttibulosa. 



Bougainvillea 7-amosa liberates the medusoid Margelis rainosa. 



Cordylophora lacustris and Tubularia larynx have sessile gono- 

 phores. 



The second type includes Campanularians, Sertularians, Plumularians, 

 and others, in which the protective sheath surrounding the colony is 

 continued into little cups enclosing the polypes (calyptoblastic). The 

 free medusoids have their gonads placed in the course of the radial 

 canals (Leptomedusce), and are either "ocellate" or "vesiculate." 



