3l6 COELENTERATA SCYPHOZOA chap. 



other features of their radial symmetry, the jelly-fish frequently 

 exhibit duplication or irregular variation of the radii.^ 



The gastric pouches may extend to the margin of the disc, 

 where they are united to form a large ring sinus, or they may be 

 in communication at the periphery by only a very narrow x^assage 

 (Cubomedusae). In the Discophora the gastric pouches, however, 

 do not extend more than half-way to the margin, and they may 

 be connected with the marginal ring-canal by a series of branched 

 interradial canals. Between the gastric pouches in these forms 

 branched perradial canals pass from tlie gastric cavity to the 

 marginal ring canal, and the system of canals is completed by 

 unbranched " adradial " canals passing between the perradials and 

 interradials from the sides of the gastric pouches to the ring- 

 canal (Fig. 143). 



In the Discophora there are four shallow interradial pits 

 or pouches lined by ectoderm on the under side of the umbrella- 

 wall. As these pits correspond with the position of the gonads 

 in the gastric pouches they are frequently called the " sub-genital 

 pits." In the Stauromedusae and Cubomedusae they are con- 

 tinued through the interradial gastric septa to the aboral side of 

 .the disc, and they are generally known in these cases by the name 

 " interradial funnels." The functions and homologies of these 

 ectodermic pits and funnels are still uncertain. 



The Scyphozoa are usually dioecious, but Chrysaora and 

 Lincrgcs are sometimes hermaphrodite. The female Medusae 

 can usually be distinguished from the male by the darker or 

 brighter colour of the gonads, whicli are band -shaped, horse- 

 shoe-shaped, or circular organs, situated on the endoderm of 

 the interradial gastric pouches. They are, when nearly ripe, 

 conspicuous and brightly coloured organs, and in nearly all 

 species can be clearly seen through the transparent or semi- 

 transparent tissues of the disc. The reproductive cells are dis- 

 charged into the gastric cavity and escape by the mouth. The 

 eggs are probably fertilised in the water, and may be retained 

 in special pouches on the lips of the manubrium until the 

 segmentation is completed.^ Asexual reproduction does not 

 occur in the free -swimming or adult stage of any Scyphozoa. 

 In some cases (probably exceptional) the development is direct. 

 In Pelagia, for example, it is known that the fertilised egg gives 



i See note ^ p. 312. ^ g. A. Minchiii. Proc. Zool. Sue. 1S89, p. 583. 



