170 THE OCEAN WORLD. 
spheres. These eggs.are transformed into oval larve, covered with 
vibratile cilia, having a slight depression in front. They swim about 
for a short time with great activity, much like some of the Infusoria, 
which they strikingly resemble in other respects. 
At the end of forty-eight hours their movements decrease. Aided 
by the depression already noted, the larval form attaches itself to 
some solid body, fixing itself to it at this stage by the presence of a 
thick mucous matter. A change of form soon takes place: it becomes 
elongated; its pedicle is contracted, and its free extremity swells into 
a club-like shape. An opening soon presents itself in the centre of 
this extremity, through which an internal cavity appears. Four little 
protuberances have now appeared on the edge, which are in time 
elongated in the manner of arms. Others soon follow: these are the 
tentacles of a polyp: the young infusorian has become a polyp ! 
The polyp increases by buds and shoots, just like a strawberry 
plant, which throws out its slender stems in all directions, covering 
all the neighbouring ground. 
The young Medusa lives some time under this form. Then one 
of the polyps becomes enlarged and its form cylindrical. This 
cylinder is divided into from ten to fourteen superimposed rings. 
These rings, at first smooth, form themselves into festoons, and 
separate into bifurcated thongs; the intermediate lines become 
channeled. The animal now resembles a pile of plates, cut round 
the edges. Ina short time each ring is slightly raised at the free 
edge of its fringe: this then becomes contractile. The rings are 
individualised. Finally, these disc-shaped creatures isolate them- 
selves. When detached, they begin to swim: from that time they 
have only to perfect and modify their form. From being flat, they 
become concave on the one side and convex on the other. The 
digestive cavity-—the gastro-vascular canals—become more decided ; 
the mouth opens on the concave surface; the tentacles are elongated; 
the floating marginal cirri become more and more numerous; and 
now, after all these metamorphoses, the Medusa appears ; it perfectly 
resembles, not the parent form, but that from which its parent 
form originally sprung. 
