240 



The second form of appendage, the yonophores, usually possess a 

 bell-shaped mantle containing circular and radial vessels, and surround- 

 ing the central stalk or clapper (manubrium), which is filled with 

 ova or spermatozoa. They usually arise in clusters at the base of the 

 tentacles, more rarely from the nutritive Polyps themselves (e.g. in 

 Veletla). The male and female generative products always arise 

 separately in differently shaped buds, but are usually found closely 



approximated on the s; HU 

 stock (fig. 186). There are, 

 however, also dioecious Sipho- 

 nojihora, or if the niedusoid 

 buds or gonophores be regarded 

 as generative organs, Siphono- 

 phora of distinct sexe s , e.g., 

 Apolemia uvaria and Diphycs 

 acvminctta. The ripe sexual 

 Medusoids frequently become 

 separated from the ttock, {.-?. 

 after the development of 'the 

 generative products, and only 

 rarely become liberated as 

 small Medusae (Chrysomitra in 

 the Velellidce), which produce 

 generative products durirg 

 their free life. 



Besides the constant nutri- 

 tive Polyps and medusoid 

 gonophores, there are incon- 

 stant appendages, which are 

 also modified Polypoids or 

 Medusoids. These are the 

 mou-thless worm-like dactylo- 

 zoids (fig. 186), which, like 

 the Polyps, are provided with 

 a tentacle, which is, however, 

 shorter and simpler, and has no lateral branches or aggregations 

 of nematocysts; also the leaf-shaped hard cartilaginous hydrophyUi<i, 

 which serve to protect the polyps, dactyloaoids, a-nd gonophores ; and 

 finally the appendages known as nectocalyces, which are placed beneath 

 the pneumatophore. The nectocalyces ha-ve a structure similar to 

 that of the Medusre, though their bilateral symmetry is apparent ; 



NK 



PIG. 189. Small larval stock of Ago 7m O;>.<H'S after 

 the type of Athorylia. Lf, Pneumatophore ; 

 D, liydrophj-llium ; Nk, groups of nemato- 

 cysts ; P, polyp. 



