CHAPTER VII. 

 SUB-CLASS DISCOPHORA. 



THE group of Hydrozoa here spoken of as Discophora or 

 Medusidae comprises most of the familiar organisms known to 

 visitors at the sea-side as sea-jellies, jelly-fishes, or sea-nettles ; 

 this last name being derived from the power possessed by 

 some of them of stinging pretty severely in virtue of the pos- 

 session of numerous thread-cells. Under the name, however, 

 of sea-jellies are included a number of large organisms, ex- 

 tremely common at certain seasons in our seas, but now 

 known to be properly referable to another group of the Hy- 

 drozoa (viz., Lucernarida). It is these large forms which 

 alone possess any power of stinging man, and to these the 

 term of " sea-nettles " ought properly to be restricted. They 

 are better known under the name of " hidden-eyed " Medusae, 

 applied to them by the late Edward Forbes. Under the 

 present group of the Discophora are included only a number 

 of small jelly-fishes, found in great abundance at certain 

 times, floating in the open sea, but nevertheless very little 

 known to the general public in consequence of their very 

 minute size. These delicate and diminutive organisms were 

 originally described by Edward Forbes, for reasons to be 

 immediately stated, as the " naked-eyed " Medusae. It is now 

 known, however, that most of these naked-eyed Medusce are 

 in reality nothing more than the free-swimming generative 

 buds, or medusiform gonophores, produced by budding from 

 so many of the other Hydrozoa, and then detached, as we 

 have formerly seen, to lead an independent existence. That 

 this is their true nature, is shown by the fact that the eggs 

 which they produce develop themselves, not into fresh Me- 

 dusce, but into various other forms of Hydrozoa, which are 

 fixed or oceanic. Under these circumstances, therefore, the 



