134 THE OCEAN WORLD. 



cavity of the polyp, 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 be perceived through the transparent 

 membranous envelope. From this position they escape from the 

 mouth 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 ; more- 

 over, 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 polyp 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 mammillations 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 polyp is 



represented fixed upon a bryozoa, 

 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 shows the successive 

 forms of the young polyps in 

 the progressive phases of their de- 

 velopment being a young coralline 



polyp fixed upon a rock still con- 

 Fig. 55. Very young Polyps, attached to a . , ,. \- . ., , 



Bryozoa. tracted. Fig. 57 is a similar coral- 



line attached to a rock and expanding 



its tentacula. Fig. 58 represents a small pointed rock covered with 

 polypi and polypidoms of the natural size and of different shapes, but 



