68 CORAL AND ATOLLS 



rested temporarily on its sides. These wandering larvse, 

 though they hve for several weeks, undergo no development. 

 They never attain tentacles, they acquire no skeleton, and yet, 

 if fixation does at length occur, it provides the necessary 

 stimulus, and growth and development proceed vigorously even 

 under unfavourable circumstances. A larva may in this 

 period of non-development be carried far by currents, and 

 it is evidently an important factor in the economy of corals 

 that this stage of developmental inactivity should last long in 

 some members of the brood, for thus the chances of the spread 

 of a species become greatly increased. On the other hand, 

 a larva may never wander from its parent colony ; but may 

 settle on some exposed portion, and start a new colony of its 

 own upon its parent growth ; or it may settle down in the 

 company of a fellow, or several of its fellows, and start a 

 compound colouy which is in every respect similar to a growth 

 that is the outcome of the activity of a single larva. 



With the fixation of the larva a new phase commences in 

 the life of a coral : the forvvardly pointing end of the swimming 

 larva now becomes its point of attachment, and it expands 

 laterally to form the basal plate : the dimple of the mouth 

 opens up to form the stomodeum, and the original solid larva 

 becomes hollowed out by a central cavity. The animal 

 becomes more complex, but into the precise steps of this 

 differentiation of parts it is not necessary to enter ; tentacles 

 are budded out, mesenteries are formed in definite order, and 

 the larva assumes the form of the adult zooid. 



Calcium carbonate is laid down as the supporting skeleton, 

 which in the end becomes " coral " in the popular sense of the 

 word, and soon the pioneer commences the process of asexual 

 reproduction by budding or by fission, and so lays the 

 foundation of the complex body of the coral colony. 



