460 



Charles R. Stockard 



three, four and five new arms. These differences in rates are 

 significant when compared with their probable errors. 



Secondly, it is to be noted that the average of final disk diameters 

 in Ophiocoma echinata is practically equal in all of the groups. 

 This fact might be reconciled with the smaller increase in disk 

 diameters shown in the more injured groups of Ophiocoma riisei, 



TABLE IX 



Tabulated summary showing the rates of regeneration in brittle-stars when regenerating (liferent numbers 



of arms 



Ophiocoma riisei 



Ophiocoma echinata 



where the rate of regenerative growth is the same in all groups, 

 by supposing that the decrease in growth rates of arms in more 

 injured individuals of Ophiocoma echinata is sufficient to allow the 

 disk to increase in size as readily as those disks which are growing 

 only a few arms but at a more rapid rate of regeneration. In 

 Ophiocoma echinata arms grow 30 per cent faster in those speci- 

 mens regenerating only one arm than in those growing five. It is 

 admitted, however, that the actual amount of regenerating tissue 



