Studies of Tissue Growth 465 



move to surround the prey and are not entirely passive but prob- 

 ably in comparison with the disk tissue use a proportionate share 

 of the available material in starved individuals. It would seem 

 in consideration of the great loss in size that the new regenerating 

 arms require an unusually large amount of nutriment. The 

 medusae growing six new arms, for example, show a much greater 

 decrease in the size of their disks over those growing two new 

 arms than would be balanced by the difference in amounts of new 

 tissue in the two cases. In other words, the regenerating tissue, 

 if it be the real cause of loss in body size, exerts a peculiarly great 

 exhaustive influence. The influence is in fact almost malignant 

 in nature. 



The brittle-stars do not fall completely into line with the above 

 discussion but on closer examination they also seem to supply 

 facts in this direction. In Ophiocoma riisei the rates of regenera- 

 tion for individual arms in specimens injured to various degrees 

 are practically equal (Table IX). The influence of the new tissue 

 would be expected to show itself most markedly in the specimens 

 growing many arms and gradually less in those growing fewer. 

 This is found to be a fact. All individuals were feeding and grow- 

 ing during the experiments but those regenerating five arms in- 

 creased least in size although they had the smallest total amount 

 of tissue to feed and those growing only one or two arms increased 

 most. 



The other species of brittle-star, Ophiocoma echinata, regen- 

 erates each arm at a rate varying inversely with the extent of injury. 

 When five arms are regenerating each arm grows only 78 per cent 

 as fast as when only one arm is being regenerated. The increase 

 in size of these ophiurans was uniform in all the groups. A pos- 

 sible adjustment of this fact to accord with the medusa and Ophio- 

 coma riisei might be accomplished by assuming that the more 

 rapid growth of the smaller number of arms inhibited the general 

 body increase in size to the same extent as did the larger number 

 of less rapidly regenerating arms. By increase in size is meant 

 the increase in the disk size. When several appendages are re- 

 moved there is less tissue to draw on the food supply and the disk 

 might be expected to increase more rapidly in size under such a 



