C(ELENTEBATA. 27 



which stage it is known as the " hydra tuha" (Scyphistoma), which 

 by budding gives rise to colonies of " Hydriform polypi ;" some of 

 these assuming the form of a pile of cups placed one within the 

 other, is now called a " strobila ;" then the cups separating, each 

 becomes a free-swimming disk [ephyra], by degrees acquiring the 

 adult form. 



*Hexarhizites. 



Order II. MONOSTOMEA. 

 PELAGIADA. 



Polypite single. A central mouth. The disk with marginal 

 tentacles, or if without them with tentacles under the disk. 



The reproductive elements are developed in the disk, or by 

 fission from a fixed trophosome, and, in their detached condition, 

 grow with great rapidity, ultimately attaining a weight of many 

 hundreds of pounds. Cyanaa arctica has been found with a disk 

 seven feet in diameter and with tentacles fifty feet long, the fixed 

 trophosome from which it proceeded being of very small size. 



Pelagiida. Cyaneida. 



Pelagia. Cyanea. 



***"> 



Aurelia= Medusa. 



Order III. CALYCOZOA. 



PODACTINARIA. LUCERNARIIDA. 



Polypite single, in the centre of a cup-shaped umbrella, its 

 proximal end fixed. Generative elements discharging themselves 

 into the body-cavity. 



The umbrella is eight- or nine-lobed in Lucernaria, each lobe 

 bearing a tuft of tentacles ; in Carduella they form one con- 

 tinuous series. " The whole organism is semitransparent, variously 

 coloured, and of a gelatinous consistence." 



