10 DESCRIPTIVE CATALOGUE OF THE 



halves. The plane of symmetry extends through the axis of the animal and 

 the marginal body. The number of flaps in each such part is variable. It 

 will be seen from this that if there are a marginal bodies ( = 4-) and 6 

 flaps in each symmetrical part of an autimer, that there will be congruent 

 autimers ; 2, symmetrical parts ; and 26 marginal flaps on the umbrella. 



The number x is generally 2 that is to say, that there are eight marginal 

 bodies and autimers each with at least two, often four or more flaps. The 

 The number x may, however, be 1 (Cubamedusse), or greater than 2 (Collaspis, 

 Bolycloiiida?, &c.). 



2. In all Scyphomedusa?, with the exception of the Rhizostomse, tentacles 

 are developed, which grow out from the lower side of the umbrella near the 

 margin ; an exception is Aurelia. These are present also in the corresponding 

 part of Lucernarida?, and their number is very variable ; they may be very 

 numerous. The tentacles are solid or hollow, and in that case the canal which 

 extends through them is in connection with the gastravascular system. 



A kind of longitudinal chorda is developed along one side, and there are 

 longitudinal striated muscular fibres in the ectodermal sub-epithelium. 



The tentacles are studded with cuidablasts. 



Their movements are very extraordinary, they can be contracted to one 

 hundredth part of their length when expanded. 



3. The marginal bodies referred to above, which are absent in the Lucer- 

 narida?, are hollow cylindrical organs. The cavity is in communication with 

 the canal system, and clothed with indifferent entodermal cells. Their outer 

 surface is covered by differentiated ectoderm cells. The distal end is invariably 

 occupied by a heap of otoliths. Further down pigment spots are frequently 

 developed, which indicate the presence of an organ of sight. In Euhomedusse, 

 &c., this structure becomes very complicated, and five eyes with lenses, &c., can 

 be distinguished on the marginal body (Charybdea, Glaus). The narrow sensi- 

 tive cells of the ectoderm are in connection with subepithelial ganglia cells. 

 Often a conical depression is observed on the dorsal side of the umbrella just 

 above the marginal body in which radiating folds and nerves (1) have been 

 observed. Sometimes, also, complicated folds are formed at the base of the 

 marginal body, and here sensitive cells and ganglia cells have been observed 

 (Cyanea v. Lendenfeld). From the marginal bodies, nerves radiate towards 

 the centre of the disc. These are situated on the lower side of the umbrella, 

 just below the epithelial surface layer of cells in the adult (Cyanea v. Lenden- 

 feld). 



4. Systems of muscles are observed in the comparatively thin lamella 

 which covers the stomach cavity. Also these are produced in the first 



