Rate of Regeneration in Cassiopea xamachana. 87 



gradually decreasing in size, probably due to an insufficient food supply. 

 It should be recalled, however, that Morgan has shown for a number of 

 forms that starvation or lack of food does not affect the rate of differentia- 

 tion in the regenerating processes. Further, all animals in my experi- 

 ments were under identical conditions, so that they are to be compared 

 without regard to food supply. The fifth, seventh, and ninth columns 

 give the specific amounts of regeneration at the times indicated. In these 

 tables it is unnecessary to calculate a specific rate of regeneration per day, 

 since the growth was continuous and each column of specific amounts is 

 given for a certain number of days ; obviously the specific amounts divided 

 by the same number of days are to one another as their quotients would 

 be. Thus the first column of specific amounts not only indicates the 

 specific amounts of regeneration for each individual up to that time, but 

 also the relative rates of growth during the 20 days. 



At 20 days after the operation one individual with only one mouth- 

 arm removed and both medusae with two arms removed have regenerated 

 faster than any of those with four or five removed arms. The ones having 

 lost six and seven arms show faster regeneration than any others of the 

 series. These four medusK are, however, the smallest individuals, and 

 young small medusae usually regenerate faster than larger ones, even under 

 the same conditions. The medusae with four alternate arms removed are 

 going at about the same rate as the two above with four adjacently cut 

 arms. All medusa; in the table, with the exception of the last two, had 

 consecutive or adjacent arms removed. 



After 23 days the medusae have decreased somewhat in size, as is 

 shown by comparing the second and fourth columns. At this time, July 

 6, the fifth column, specific amount, shows a sudden jump when com- 

 pared with the third column. This is not an actual jump occurring within 

 the three days' time between the calculations, but is only apparent, since 

 the specific amounts after 20 days were calculated on the basis of the 

 original diameters of the medusae and the calculations at 23 days are made 

 on the diameters at this time.^ The two columns are not to be compared. 

 The other columns to the right are open to comparison, since the diameters 

 were remeasured each time. The specific rates of regeneration for the 

 individuals with one, two, and three arms removed are about the same. 

 Those with four removed arms have a slight advantage over those having 

 lost five arms ; it must be mentioned, however, that one individual with 

 five arms removed has failed to produce a bud from one stump and conse- 

 quently its average regeneration is abnormally low. Again the ones with seven 

 cut arms are regenerating fastest of all, and those that lost six follow next. 



On the i8th of July, 35 days after the operation, the regenerating buds 



^ Recent studies show that only the original diameters are to be used in such cal- 

 culations, as final diameters vary with different extents of injury. 



