THE OCEAN WORLD. 
cavity of tlie polypes, where they can be seen through its transparency, 
as exhibited in Fig. 54. Aided by the magnifying powers of the 
microscope, coral larvae may here he perceived through the transparent 
membranous envelope. From this position they escape from the 
month of the mother in the manner represented in the upper branch. 
The animal then resembles a little white grub or worm, more or 
less elongated. The larva is, however, still egg-shaped or ovoid ; 
moreover, it is sunk in a hollow cavity, and covered with cilia, by 
the aid of which it can swim. Sometimes one of its extremities 
becomes enlarged, the other remaining slender and pointed. Upon 
this an opening is formed communicating with the interior cavity : 
this is the mouth. The larvae swim backwards ; that is to say, with 
the mouth behind. 
It is only at a certain period after birth that the coral polype fixes 
itself and commences its metamorphoses, which consist essentially in 
a change of form and proportions. The buccal extremity is diminished 
and tapers off, whilst the base swells, and is enlarged — it becomes 
discoid ; the posterior surface of this sort of disk is a plane, the front 
representing the mouth, at the bottom of a depression edged with a great 
cushion. Eight mammals or swellings now appear, corresponding to 
the chambers which divide the interior of the disk: the worm has 
taken its radiate form. Finally, the mammals are elongated and 
transformed into tentacula. In Fig. 55 a young coral polype is 
its tentacula. It also represents a small pointed rock covered with 
polypes and polypiers of the natural size and of different shapes, but 
Fig. 55. Very young Polypes, attached to a 
Bryozoare. 
represented fixed upon a bryozoare, 
a name employed by Ehrenberg for 
zoophytes having a mouth and anus. 
It forms a small disk, the fortieth 
part of an inch in diameter, and 
having its spicula already coloured 
red. Fig. 56 show's the successive 
forms of the young polypes in 
the progressive phases of their de- 
velopment — being a young coralline 
polype fixed upon a rock still con- 
tracted. Fig. 57 is a similar coral- 
line attached to a rock and expanding 
