TYPES OF CCELENTEKA--AUREI.IA Af'RlTA. 149 



cavity, are four groups of mobile gastric filaments (g.f. t Fig. 

 68), which are very characteristic of jelly-fish. In appear- 

 ance these are very similar to the small tentacles of the 

 margin, and, like them, are hollow. They are covered with 

 endoderm with ciliated, glandular, muscular, and stinging 

 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 epi- 

 thelium, situated on the 

 four patches already men- 

 tioned, within sacs which 

 are derived from and com- 

 municate with the floor of 

 the gastric cavity. They 

 are of a reddish violet 

 colour, and at first of a 

 horseshoe shape, with the 

 closed part of the curve 

 directed outwards. After- 

 wards the ridges become 

 circular, and surround 

 the walls of the sacs in which they lie. But the sub- 

 umbrellar surface is modified beneath each genital sac in 

 such a way that the sac comes to lie in a sub-genital cavity 

 communicating with the exterior (g.p., Fig. 68). The con- 

 tractions of the umbrella produce a rhythmic movement of 

 the water which enters the sub-genital cavities, and this 

 constant renewal of the water suggests some respiratory 

 significance for the sacs. The genital sacs containing the 

 plaited ridges of germinal epithelium communicate with the 

 gastric cavity only, while the sub-genital cavities containing 

 water and enveloping the genital sacs communicate with the 

 exterior only. 



The ova and spermatozoa pass from the frills of germinal 



FIG. 68. Vertical section of 

 After Glaus. 



;//.. Mouth ; st., stomach ; r.c., radial canal ; 

 A\, reproductive organs; g.f., gastric- 

 filaments; -./., sub-genital cavity ; /., 

 marginal tentacle ; j>\, sense organ ; 

 the shaded part is mesoglcea. 



