88 Papers from the Marine Biological Laboratory at Tortugas. 



certain that the Millepora must have, on account of its more rapid growth, 

 covered over and destroyed the Uving tissue of the colony. 



A skeleton thus incrusted with Millepora, which was complete in struc- 

 tural detail in July 191 1, had by August 1912 been reduced to about one- 

 third of its original height. Nothing of the Gorgonia skeleton beyond the 

 stouter branches remained . The whole of the ' ' leaf ' ' had been broken down , 

 presumably by the weight of the incrusting Millepora. 



The previously mentioned hurricane was, as had been pointed out in 

 dealing with the growth-records, sufificiently prolonged to destroy almost 

 every young gorgonian which had become attached during the breeding- 

 season of that year. No evidence could be secured to determine whether 

 the destruction took place by an actual washing of the colonies from their 

 attachment or by the shifting of the easily movable material — algae, sedi- 

 ment, shells, and even quite large fragments of coral rock — which by filling 

 up all cracks in the surface of the reef would have been sufficient to smother 

 the small individuals. 



Gorgcnians growing upon the shallow reefs are, with more or less regu- 

 larity, subjected to exposure to the air. In summer the uncommonly low 

 spring-tides (when the low full-moon tide comes in the late afternoon) most 

 frequently come on calm days, when the exposure is most destructive. On 

 June 6 and 8, 1910, and again on July 23, 191 1, all of the shallow reefs were 

 exposed for a space of time sufficient to destroy the superficial tissues of most 

 corals and gorgonians which grew on the highest part of the reefs. While 

 all of the species of gorgonians studied suffered to a greater or less extent, 

 the injuries were most severe in the case of G. flahellum and G. acerosa. 

 Frequently there resulted the death of the distal half of the colony which, 

 within a few days after its exposure to the air, would slough off from the 

 uninjured proximal part. Plexaura and Eunecia were much less frequently 

 injured, the latter in only two observed instances, and then only after pro- 

 longed exposure. The ability of the two last-mentioned forms to withstand 

 the exposure is at least correlated with, if not dependent upon, the thickness 

 and toughness of the coenenchyma into which the polyps may be retracted 

 when the colony is exposed. 



In all observed instances of injury from exposure to the air the uninjured 

 portions of the colony showed no ill effects from the injury of the distal 

 portion and their growth was at least as rapid as in an uninjured specimen. 



REGENERATION EXPERIMENTS. 

 The injuries occurring in nature are so variable and are besides so entirely 

 uncontrollable that a series of experiments was undertaken in order to secure 

 more definite data concerning the capacity for regeneration in these animals. 

 All of the experiments here described were extensive in nature, usually 

 involving skeleton and coenenchyma as well as the polyps. In short, they 

 were made to simulate the injuries to which the gorgonians are subjected 

 under natural conditions on the reefs. 



