THE DISCOPHORA. 



121 



In striking contrast with the complexity of these repro- 

 ductive processes, the gonophore is represented, in Hydra, 



Fig. 17.— Willsia, sp. : A, the medusa, with budding stolons. B, one of the buds 

 developed on a stolon ; h, radial canal of the nectocalyx ; e, manubrium. C, a 

 stolon: g, its free end beset with netnatocysts ; b, c, d, budding medusoids ; 

 /, medusoid nearly ready to be detached ; e, its manubrium ; d, its nectocalyx 

 A, a radial canal. 



by a mere enlargement of the body-wall, situated close to the 

 bases of the tentacula, in the case of the testes, and nearer 

 the attached end of the body in that of the ovary. The ovary 

 develops a single ovum, which, as Kleinenberg has shown, 

 undergoes division and invests itself with a chitinous coat 

 while still attached to the body of the parent. This chiti- 

 nous investment is more or less spinose, and is often con- 

 founded with an egg-shell. It obviously answers to the 

 perisarc of a Tubularian, and its presence in the embryo of 

 the Hydra, in which no perisarc is developed by the adult, 

 suggests that Hydra may not represent the simplest primary 

 condition of a Hydrophoran, but may be a reduced modifica- 

 tion of a Tubularian. 



2. The Discophora. — These " Medusae " resemble the 

 more perfect free medusoid gonophores of the Hydrophora, 

 in so far as they consist of a hydranth or polypite attached 

 to the centre of a gelatinous contractile swimming disk. But 

 they differ from the medusoids of the Hydrophora, inasmuch 

 as they are developed either directly from the impregnated 

 ovum ; or by gemmation from a Medusa which arises in this 

 6 



