SCYPHOMEDUS.E OF THE AUSTRALIAN SEAS. 



4. MORPHOLOGY OF THE SCYPHOMEDUS.E. 



The adult Scyphomedusre are for the most part large, disc-shaped, free- 

 swimming animals which are found in the sea. At breeding time many, 

 particularly the Rhizostauridse, swim up the rivers for some distance (Tajo, 

 Parramatta, &c.), but never leave the salt or brackish water. No Scypho- 

 mecluste have hitherto been found in fresh water. Certain forms, the Lucer- 

 narida;, attach themselves at the aboral pole, and a similar sessile mode of 

 life has been observed in certain Rhizostamidse by Keller and others. 



The Luceniaridse resemble Scyphystomas very closely. No extensive disc- 

 shaped umbrella filled with mesodermal gallert tissue is observed in them. 



All the other Scyphomedusaj possess a large disc, which forms the bulk of 

 the body above the stomach. This is termed the umbrella. 



The Scyphomedusa? are radially symmetrical animals, and resemble in 

 this particular the Echinodermata so closely that many of the older authors, 

 and particularly L. Agassiz, combined the Scyphomedusse, corals, etc., with 

 the Echinoderma to form one group the radiata. This classification can, 

 however, not be retained in view of the great anatomical differences between 

 these two, and it is not accepted at the present time. 



The radii are not of equal morphological value, and it is easy to recognize 

 that the organs are always in fours, forming a cross at the beginning 

 (Scyphystoma), and that afterwards multiples of four are added to these. 

 The mouth has always the shape of a cross, and the four radii which pass 

 through the dilated corners of the mouth are known as the primary radii. 

 They are vertical on each other. Between these, and cutting them at angles 

 of 45, there are four other radii to be distinguished, which gass through the 

 sexual organs ; these are the secondary radii. Between these eight again 

 other radii of particular interest make their appearance ; these are eight in 

 number, and termed the tertiary radii. They cut the adjacent primaries and 

 secundaries at the angle of 22 30'. 



The fundamental form of the Scyphomedusre is that of a tetramer amphi- 

 tect pyramid. 



The body of an. adult Scyphomedusse consists of the following parts : 

 1. A large circular disc or bell-shaped umbrella, which is very thick, and 

 in the lower portion of which there extends a flat cavity, the stomach. The 

 margin of the umbrella is serrated, flapped, or otherwise broken. The margin 

 always is perfectly symmetrical. There are 4 x organs of sense the 

 Lucernaridfe are destitute of these marginal bodies situated in indentures 

 of the margin, and the margin consists of as many congruent autimers 

 as there are marginal bodies. Each of these consists of two symmetric 



