542 DR. F. W. JONES ON GROWTH-FORMS [Juiie 18, 



substance, and here too, the sympathetic reaction of the zooids is 

 shown. The tunnels destroy whole groups of zooids and replace 

 the solid skeleton of the coral by a series of tubes, and the sti'ength 

 of the whole colony is greatly diminished ; around these tubes the 

 uninjured zooids divide and grow with increased activitj^, new 

 calcium carbonate is thrown out, and an attempt is made to com- 

 pensate for the destruction of tissue caused by the worm. Some 

 curious results are brought about in this way, and specimens in 

 which worm-boring has led to fantastic growth are always to be 

 found, for few corals escape their inroads. A tunnel running 

 superficially, or in the thickness of a plate-like growth, leads to 

 an increased activity of surface-growth of the zooids, and the 

 tunnel stands out boldly from the surface, covered and strengthened 

 by an ever advancing layer of coral. In this way a tunnel may 

 actually bridge a space from one plate to another, and its moutli 

 be carried out clear of the general surface of the coral, for where 

 the tunnel goes the surface-layer of coral ever keeps pace. 



(B.) The question of the processes of i-epair becomes farther 

 complicated in those corals, such as the Madrepores, in which all 

 the members of the colony are not of equal importance. We have 

 seen in considering the mode of growth of such corals, that the 

 very first individual in a colony may continue to flourish and lead 

 the oTowth of the entire community as long as that community 

 lasts. The original zooid that, as an embryo, settled on the basis 

 that formed the site of growth maybe the '^directive" zooid of 

 the entire colony, and the apical zooid may represent the oldest 

 livino- animal matter in the community. But besides the 

 " directive apical zooid," others arise at intervals by budding 

 from the sides, that are possessed of more inherent vitality than 

 their fellows, and from their first birth they tend to grow out as 

 new directive zooids and lead to lateral branch formation — and 

 besides these more virile lateral zooids are the hosts of individuals 

 that in the normal condition of the growth reach no greater 

 dignity than a uniform projection of their corallites. 



IsTow when injury or destruction affects a portion of the colony, 

 it reacts on individuals whose functionating values in the economy 

 of the colony are not equal, and so we should expect that the result 

 of injury or destruction would vary according to the different 

 pai-ts of the colony on which the maximum of damage falls. And 

 this is the case. The actual results of repair of various injuries 

 inflicted in experiment, or by Nature, will show more clearly the 

 relative values and functional activities of diflerent portions of 

 such a colony, than will any amount of theorising or speculation. 



1. If the injury be so inflicted that the branch of a Madrepore 

 colony is broken transversely, and the injury is limited to a mere 

 fracture of the cross section, then the repair takes place by the 

 activity of the " apical directive zooid." 



There is as we have seen, no portion of a Madrepore colony 

 that normally dies, and the obliteration of animal tissues in the 



