Studies of Tissue Growth 459 



The upper half of Table IX summarizes the data from O. riisei 

 and presents the following points of interest. First, individuals 

 of Ophiocoma nisei when kept under identical conditions increase 

 in body size the slower the more arms the individual is regenerating. 

 This fact is not likely due to the incapacity of the more injured 

 specimens to secure food since the compartments in which all 

 were confined are small and the individuals seemed equally able 

 to traverse this limited feeding ground. A probable explanation 

 is that the new regenerating tissue possesses an excessive capacity 

 for the assimilation of nourishment and consequently those speci- 

 mens regenerating more new arms were less able to increase in 

 body size than those regenerating fewer. 



Table IX shows secondly, that the rate of regeneration of each 

 arm bears no relation to the number of regenerating arms, or in 

 other words, the extent of injury. 



Column five gives the specific amounts of regeneration for each 

 arm when calculated by dividing the average arm lengths by 

 the final disk diameters. The last two figures in the column indi- 

 cate the error of such calculation. Calculating the specific 

 amounts of regeneration on the basis of the original average diam- 

 eters which were practically equal in all the groups we obtain a 

 series of numbers bearing the same relations to one another as are 

 shown by the numbers in column four. 



Ophiocoma echinata, a spiny, grayish, mottled brittle-star, was 

 experimented upon in exactly the same fashion as Ophiocoma 

 riisei. Its response to different degrees of injury was much more 

 pronounced than that of the species riisei. Again five groups of 

 individuals of the same average size were selected and operated 

 upon so as to remove difi^erent numbers of arms i cm. from their 

 bases at the disk. 



Referring again to Table IX the lower half represents a tabulated 

 summary of the data from Ophiocoma echinata. Two facts of 

 importance are here also to be recognized. First, the fourth 

 column giving the average arm lengths for each group shows that 

 the rate of regeneration decreases as the extent of injury increases. 

 Each new arm grows fastest from those individuals regenerating 

 a single arm and successively slower in the groups growing two, 



