THE DISCOPHORA. 



121 



In striking contrast with tlie complexity of these repro- 

 ductive processes, the gonophore is rej^resented, in Hydra^ 



FiQ. n.— Willsia, sp. : A, Ihe merlnsa. with buddinff stolons. B. one of the buds 

 developed on a stolon ; h, radial canal of the nectocalvx; f, manubrium. 6'. a 

 stolon; !7, its free end beset with nematocyst? ; 6, c, d, budding medusoids ; 

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

 /i, a radial canal. 



by a mere enlarg-ement of the bod^'-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 sino-le 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 cliiti- 

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

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

 2')erisarc of a Tubularian, and its presence in the embryo of 

 the Ili/dra^ in which no perisarc is developed by the adult, 

 suggests that Ili/dra may not represent the simplest primary 

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

 tion of a Tubularian. 



2. The DiscopnoRA. — These " Medusre " resemble the 

 more perfect free medusoid gonophores of the Ilydrophora^ 

 in so far as they consist of a hydrant h or polypite attached 

 to the centre of a gelatinous contractile swimming disk. But 

 they differ from the medusoids of the Ilydrophora, inasmuch 

 as they are developed either directly from the impregnated 

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



