140 



CCELENTERA. 



radial canals are straight, but the other eight are branched, 

 and thus in an adult Aurelia the total number of canals is 

 large. These canals are really due to a partial obliteration 

 of the gastric cavity by a fusion of its ex-umbrellar and sub- 

 umbrellar walls along definite lines. They are all lined by 

 ciliated endoderm. 



Where the manubrium or tube from the mouth passes 

 into the central digestive cavity, there are four strong pillars 

 of thickened sub umbrellar material. Outside each of these 



pillars, and still near the 

 base of the manubrium, 

 there are four patches 

 where the sub - umbrellar 

 surface remains thin. 

 These are the gastro-genital 

 membranes, lined inter- 

 nally by germinal epi- 

 thelium (Fig. 60, Ji.). 



To the inside of these 

 genital organs, within the 

 digestive cavity, are four 

 groups of mobile gastric 

 filaments {g.f., Fig. 60), 

 which are very character- 

 istic of jelly - fish. In 

 appearance these are very 

 similar to the small tent- 

 acles of the margin, and, 

 are covered with endo- 

 and stinging 



Fig. 59.- 



-Surface view of Aurelia.- 

 From Romanes. 



Showing four genital pockets in centre, 

 much branched radial canals, eight peri- 

 pheral niches for sense organs, and peri- 

 pheral tentacles. 



like them, are hollow. They 



derm — with ciliated, glandular, muscular. 



cells. 



The body is mapped out into regions by the following convention :- 

 The first tentacles to appear in the larva are four in number, and 

 correspond to the four angles of the mouth ; the radii on which they 

 appear are called "perradial." Halfway between these, four " inter- 

 radials'' are then developed. Then eight "adradials" may follow, 

 between perradii and interradii. 



Reproductive system. — The sexes are separate. The 

 reproductive organs — ovaries or testes — consist of plaited 

 ridges of germinal epithelium, situated on the four patches 

 already mentioned, within sacs which are derived from and 



