1907.] AND SUPPOSED SPECIES IN CORALS. 537 



avoiding injury, and though they afford some protection to the 

 more delicate parts of the zooid, a danger that threatens the 

 whole mass of the coral is a danger that the coral cannot shield 

 itself from. 



There is yet another factor in the question of the repair and 

 regeneration of corals, and it is the factor that is so intimately 

 bound up with the problem of the limitless liability of the corals 

 as a class to become modified and to vary. When a name is given 

 to this factor, and it is stated that the corals are a plastic group, 

 it is not quite easy to say what that name should rightly connote ; 

 but although the words when used in their more common sense 

 are not at all apt, I would say that the corals are an impressionable 

 and responsive class of animals. They are ready to comply with 

 the demands of their environment; they are, within narrow limits, 

 resourceful and capable of remarkable compromises between the 

 contending forces of inherent growth-form and alterations 

 demanded by changed surroundings. 



Judged as we judge the higher animals, the corals are a class 

 of unstable individuals : we can say definitely that a young 

 elephant will grow up to be an elephant and no other beast ; but 

 we cannot say that an embryo Millepore will grow to be a 

 branching M. cdcicoriiis and not a plate-like M. coviplanata or 

 M. verrucosa ; we cannot foretell that a young colony of Pocilli- 

 pora will certainly be P. hrevicornis and not P. nohilis, for, 

 depending on the conditions of its surroundings, it might chance 

 to be either. 



This very plasticity shows itself not only within the limits of 

 a certain species, but in the life of every actinozooid, for each 

 member of a colony, or each solitaiy coral, shows in its life, its 

 growth, and its repair, all those endless conformations to the 

 demands of its environment that tend to produce change through- 

 out the whole world of living things. An actinozoon, then, as an 

 individual, possesses a birthright that gives it a maximum power 

 of repair of damage, or regeneration of lost ]3arts ; and in the 

 colonial forms, which are of special importance in the economy of 

 the class, this power is greatly intensified. 



In the group of solitary corals there is no very great interest 

 attached to the processes of repair. The individual animal is at 

 times damaged by injury, and the damage is repaired by the 

 laying down of new calcified material, causing an irregularity in 

 the symmetry of the animal. As a common feature of repair in 

 any living thing, it may be noticed that the new material laid 

 down tends to be excessive ; and few large Fungise are to be found 

 in which some injury has not caused the development of a 

 quantity of irregvilar calcification, where the delicate tissues of 

 the animal have been split over the sharp edge of one of the rays. 

 Excessive injury leads to local death, and local death may affect 

 a very large area of a solitary coral without being necessarily fatal 

 to the whole animal. The individual has but little power of re- 

 pairing a large portion of its surface when once the area is 



