DEPARTMENT OF MARINE BIOLOGY. I3I 



with most arms removed decreased most rapidly, the group having lost 8 

 arms decreased twice as much as did those from which only i arm had been 

 removed. Although the greatly injured animals were decreasing in size so 

 rapidly they produced new arm-buds at the fastest rate. From this it seems 

 that the regenerating tissue has the power to grow and assimilate material at 

 the expense and actually to the exhaustion of the original body-tissues. This 

 suggests the action of malignant growths — tumors and cancers. Such tissues 

 have an excessive capacity to absorb nutriment, and in so doing finally cause 

 the normal body-tissues to succumb. The regenerating arm-buds seem to 

 possess a similarly exaggerated capacity for absorbing nutriment from the 

 original body-parts. 



In connection with these experiments on Medusae, a large series of similar 

 experiments were tried on two species of brittle-stars common on the coral 

 reefs at Tortugas. Great difficulty was experienced in keeping these animals 

 in aquaria, but they lived and thrived in floating live-cars. These cars were 

 divided into small compartments so that the experiments might be separated. 



The experiments ran for almost 50 days, and the animals increased in size 

 and regenerated new arm-buds ranging from 25 mm. to more than 50 mm. 

 in length. The two species, Ophiocoma riisei, and a grayish form not yet 

 determined, were operated upon in similar manners so as to facilitate com- 

 parisons. Ophiocoma riisei regenerated faster than the gray species in all 

 cases. Both species regenerate their arms more rapidly when cut close to 

 the disk than when cut at greater distances away. Thus the deeper the level 

 of the cut the more rapidly will the ensuing regeneration take place. 



Individuals of both species were selected and divided into groups from 

 which different numbers of arms were removed, all arms being cut at a dis- 

 tance of I cm. from the disk. O. riisei regenerated its arms at rates entirely 

 indift'erent to the degree of injury inflicted. The gray species regenerated its 

 arms fastest when few had been removed, and distinctly slower when many 

 had been cut away. Starfish with 5 arms cut off regenerated only three- 

 fourths as rapidly as those with i arm removed and individuals having lost 

 4 arms regenerated almost as slowly as those with all 5 cut. 



These results exactly oppose those obtained from the Medusae. In both 

 cases large numbers of individuals were used and the regenerated buds were 

 long and easily measured, so that the error in the work is small. Such results 

 indicate that the influence of degree of injury is not universal and may be dif- 

 ferent in different animals. The different rates shown by the two species of 

 brittle-stars when similarly injured and kept under identical conditions are 

 suggestive in the latter regard. 



Geology of the Florida Keys and the Marine Bottom Deposits and Recent 



Corals of Southern Florida, by T. Wayland Vaughan, 



U. S. Geological Survey. 



GEOLOGICAL STUDIES. 



The excavations made during the recent extension of the Florida East 

 Coast Railway, together with the facilities afforded by the boats owned by 

 the Marine Laboratory of the Carnegie Institution offered opportunities for 

 additional observations on the geology of the Florida Kevs. I therefore ex- 

 amined many of the keys, beginning with the southern end of the cape imme- 



