456 



Charles R. Stockard 



erating arms and their rate of growth, with the possible exception 

 of those growing eight arms. Plate I strikingly illustrates this 

 decrease in size in six individuals originally of equal size, and on 

 closer examination also shows the difference in lengths of the re- 

 generated buds in the several specimens shown. 



In addition to these facts it should also be noted that the spe- 

 cific amounts and rates of regeneration when calculated on the 

 basis of the original disk diameters gradually increase from those 

 medusae growing two new arms to those regenerating eight. When 

 the specific amounts of regeneration are calculated on the basis of 

 the final disk diameters a similar but much more exaggerated 



Fig. 8 Curves indicating the decrease in size of medusae disks when regenerating different num- 

 bers of oral-arms; i, 2, 4, 6 and 8. The upper curve indicates the condition after 17 days, the 

 lower curve after 24 days. The numbers on the vertical line indicate the actual loss in diameter 

 in millimeters. 



increase is noted in those medusae growing the larger number of 

 arms. (This exaggerated increase is only apparent and is due 

 to the fact that those medusae regenerating many arms have de- 

 creased in size to a greater extent than those regenerating fewer 

 arms.) The above increases in specific amounts of regeneration 

 are, however, insignificant as is readily seen by comparing the prob- 

 able errors. The probable error of the difference between any 

 two groups may be represented by the formula 



I.e., the probable error of the difference in specific amounts of 

 regeneration between any two groups is i- or — the square root 



