200 TOILERS IN THE SEA. 



parents, and the mode of their progression greatly 

 favours this result ; thus the peculiarity of their 

 motion is liable to shorten the period of their liberty* 

 in facilitating their adherence to any object with 

 which they come into contact, by that part of their 

 body which afterwards becomes the base of the 

 polyp. When it adheres the polyp has reached 

 another stage of its existence. As soon as it becomes 

 fixed it changes its worm - like appearance, and 

 thickens, gaining in breadth what it loses in length, 

 thus shortening, and becoming discoid. The thin 

 extremity, which carries the mouth, gradually folds 

 itself back, by successive stages, until the larva 

 assumes the shape of a pin-cushion, at the summit 

 of which is the mouth. Around this orifice the 

 rudiments of the eight tentacles begin to appear, 

 which soon cover it with a pendant festoon. The 

 fixed larva thus becomes the founder of a large 

 colony. Buds form on the axis, and develop them- 

 selves into a whole nation of corals. The young 

 polypes, just hatched from the egg, are, as we have 

 seen, utterly different from their parents. They 

 must undergo many metamorphoses before they 

 reach their perfect state. These metamorphoses are 

 just the reverse of those through which insects pass. 

 The chrysalis lies immovable, but finally becomes 

 a butterfly. With the coral, the larva has the 

 power of locomotion, whereas the full-developed 



