72 COMPARATIVE ANATOMY CHAP. 



inter-radial rhopalia. 8 or 16 marginal lobes, 4 or 12 tentacles. Pcrlcotya, 

 Peripliylla. 



Sub-Order 3. Cubomedusas (Charybdeidae). 4 septa retained. 4 pair of gonades 

 on the septa, freely protruding into the gastric pouches. With 4 perradial 

 rhopalia, which contain tentaculocysts with endodermal otolith sacs, and are 

 provided with one or more eyes. 4 interradial tentacles or tufts of tentacles. 

 Mostly with velarium. CJutrybdca, Chirodropus. 



B. Mcdusce with flat, disc-like umbrella. The 4 primary gastric pouches of 

 Scyphula degenerated by disappearance of the septa, instead of which there are 8, 

 16, 32, or more radial canals of varying width, and often branched or anastomosing, 

 as survivals of the gastric cavity on the growing together of the subumbrellar and 

 exumbrellar intestinal walls. The 4 interradial gastric ridges or ttenioles are 

 retained as remains of the septa, and these carry the phacelli, or tufts of gastral 

 filaments. Development either direct with metamorphosis, or with alternation of 

 generations. In the last case an attached Sciipltula arises out of the gastrula and 

 develops into a young attached Medusa (Scyphistoma}. This multiplies in most 

 cases by a sort of repeated fission or gemmation (strobilation). The constricted 

 .!/ iltisa (Epliyra) changes through metamorphosis into the adult form. 



Sub-Order 4. Discomedusss. 



Family 1. Cannostomse. With simple mouth tube, without oral arms, with square 

 mouth, and short solid tentacles. Nausithoe (Fig. 67, p. 77). 



Family 2. Semostomae. With 4 long flag-like oral arms and cross-shaped mouth. 

 With long hollow tentacles. Pclacjia nodiluca, Cyanca, Amelia aurita. 



Family 3. Rhizostomse. Mouth grown together. With numerous small suckers 

 on the 8 long root -like oral arms ; without tentacles. Cassiopcca, Pilcma 

 (RMzostoma), Cotylorliiza, Cramlcssa, Cannorhiza (Fig. 70, p. 85). 



Sub-Class III. Ctenophora. 



Cnidaria with sensory bodies at the aboral pole ; with 8 meridional rows of 

 ciliary or ctenophoral plates, with ectodermal oesophagus. Without gastral filament?. 

 Development direct, without alternation of generations. Mesodermal jelly strongly 

 developed, with muscle, nerve, and connective tissue elements. Hermaphrodite. 



Order 1. Tentaculatse. With 2 capturing filaments with one row of simple 

 branches ; the filaments can be withdrawn into sacs situated in the lateral 

 perradii. Gastro-canals ending blindly. 



Family 1. Cydippidae. Body globular or egg-shaped. Hormiphora (Fig. 68, 



p. 79). 

 Family 2. Lobatae. Body compressed in the lateral plane, with 2 oral lobes' 



in the median plane. Euchnris. 



Family 3. Cestidae. Body band-like, compressed in the lateral plane, with- 

 out oral lobes. Ccstus. 



Order 2. Nuda. Without capturing filaments. Mouth wide, oesophagus very 

 spacious. Gastro-canals much branched and anastomosing. 

 Family 4. Beroidse. Bcroe. 



The Hydrozoa and Scyphozoa probably descend from attached forms, which are 

 only distinguished from gastrula attached by the aboral pole, either, on the one hand 

 (Hydrozoa}, by their possession of circumoral tentacles, or, on the other (Scyphozoa}, 

 by the formation of an ectodermal oesophagus. Indications of this descent can still 

 be seen in the freely swimming Hydromedusce and Scyphomedusce in their radial 



