64 CORAL AND ATOLLS 



larvae becomes more advanced, and a colony whicli at a sj)awning 

 time started by ejecting ova and sperm cells wiJl give rise, as 

 tbe season advances, to successively more perfectly developed 

 larval forms. The process of development of the larvas within 

 the zooids takes place fairly uniformly all over a colony, so 

 that any zooid that may be examined will show the larvse, or 

 reproductive elements, all in about the same stage of maturit3^ 

 The actual period over which the extrusion of larvse is spread 

 may be several days, or even a week or two, and then, after the 

 occasional appearance of a few stray individuals, the zooids cease 

 to give forth larvae, and relapse again into their normal state 

 as members of the colony. 



Zooids within the span of their lifetime are able to give 

 rise to more than one crop of germinal elements, for a seasonal 

 outpouring of the larvse does not terminate a zooid's repro- 

 ductive life. The capacity of a mature colony for reproducing 

 its species is therefore potentially very great. 



When first launched on an independent career, the young 

 coral larv<« are little bodies from 1 to 3 millimetres in length ; 

 that is to say, they are slightly longer than the diameter 

 of an average pin's head. They vary in shape according to 

 their species ; they may be oval, elongated, pear-shaped, or 

 spheroidal : moreover, the larva has some power of altering its 

 form, and, as growth proceeds, its original shape may become 

 considerably changed. 



The larvse are active motile creatures, and their activity 

 begins to display itself, as a rule, immediately after their first 

 extrusion from the parent zooid : the source of their motile 

 power is the one so commonly found in lowly swimming 

 animals — the lashing of cilia. 



The larval body is uniformly ciliated ; that is to say, it is 

 entirely covered with filamentous protoplasmic processes which 

 move in a definite manner, and urge the animal through the 

 water : the action of the cilia is wavelike, and, as a ripple of 

 fine movements, spreads down the sides of the larva, much as 

 the legs of a millipede move in their flowing sequence. 



It is by the lashing of these processes that the coral larva 



