128 



CCELENTERATA. 



External 

 Features. 



the body. It is perfectly transparent except for the four 

 gonads which are of a beautiful violet hue. 



It differs in shape from the medusoids of Obelia, for 

 it is flat, not bell-shaped. However, the general principles 

 of its construction are in <tnany respects similar. 

 It is axially symmetrical and tetramerou', i.e , 

 the peripheral parts are arranged in fours. The 

 mouth is four-cornered and opens on a short manubrium. It 

 is surrounded by four large oral tentacles which correspond 

 to the four corners of the mouth and are per-radiaL 

 The disc or umbrella is almost circular but slightly divided 



Fig. 60. — Oral View of Aurelia Aurita x 4. i^Ad nat.) 



Per-radial Canal. Tentaculocyst. Ad-radial Canal. 



Aperture 

 of Sub-_ 

 genital Pit. 



Mouth. 



into eight lobes, the indentations between them being at the 

 four per-radii and the four inter-radii. In each depression 

 or indentation there is situated a sense-organ or tentaculocyst 

 covered by a hood and having a pair of small processes or 

 lappets, one on each side. The whole border of the disc is 

 fringed by a great number of small tentacles and there is no 

 velum. 



