306 TlMEHRI. 
animals, and most markedly so in the generality of the 
lower forms, is to be found among the Hydroid Zoo- 
phytes. In many of these organisms, the special buds 
developed for reproduction do not remain attached to 
the fixed, plant-like colony, but drop off and lead a free- 
swimming existence, and increase considerably in size 
ere the sexual elements are developed. These free- 
swimming sexual organisms take the form of hemispherical 
or sub-globular bells, richly coloured, transparent and 
glassy ; and from the centre of the circular rim the true 
mouth hangs below like the clapper of the bell, while the 
edge of the gelatinous mass is fringed with a variable 
number of ribbon-like streamers, charged with stinging 
cells. They ate variously known as jelly-fishes, sea 
blubber, sea-nettles and medusae, names derived either 
from their composition, form, or stinging properties ; and 
though they are generally noticed in the ocean as floating 
inert masses, yet owing to the contractility of the bell, 
they are able to propel themselves with considerable 
rapidity through the water. These beautiful bell-like 
beings, apparently so different from a Hydroid polyp, were 
classed as widely separated organisms by the older 
naturalists to whom the history of their origin was un- 
known, but with the gradual extension of knowledge, it 
has been shewn that they produce eggs which develop, 
not into other jelly-fishes like themselves, but into fixed 
Hydroid polyps like the individuals of the colony from 
which they originally were detached. The resulting 
fixed Hydroid polyps by continuous budding give rise to 
new plant-like colonies, and these in turn produce repro- 
ductive buds which become detached and go through 
corresponding cyclical changes. 
