146 



Papers from the Department of Marine Biology. 



the first day (see figures 6, 7, 8, 9). After that time the rates of the 

 two halves gradually became more nearly equal, until at the end of an 

 experunent, if the amount to be regenerated was large, there was only a 

 slight difference between the rates of the two halves. 



In a series of experiments designed to test the importance of the time 

 factor in the difference in the rate of regeneration, sets of 10 disks each 

 were separated into halves and the sense-organs were removed from one 

 of the halves of each pair at intervals of 2 hours. It was soon found that 

 no efTect was noticeable if the centers were removed in less than 18 

 hours, and in most experiments 25 or more hours were necessary in 

 order that the rate of regeneration should be the same from each half 

 of a disk. When the second operation was made in less than 24 hours 

 from the time of dividing the disk it was impossible to distinguish 

 between such specimens and the controls from which half of the sense- 

 organs were removed at the time of the first operation. 



Table 5 shows the effect of the removal of the sense-organs from a 

 half-disk of a pair at different intervals after the separation of the disks 

 into halves, each series consisting of 10 specunens. 



Table 5. — Effect upon regeneration of the time interval between the separation of a disk into 

 halves and the removal of the sense-organs from one half. 



As shown above, the line of demarcation between the time when no 

 influence of the sense-organs will be appreciable and that after which 

 their removal has no efTect is sharply drawn at an interval of about 25 

 hours. In each series of disks there was observed the same irregularity 

 in physiological activity that was shown among the members of any 

 large series. The individuals of the highest physiological activity, 

 as shown in the rate of regeneration, were the first to show the effects 

 of the sense-organs. In any series those specunens from which the 

 sense-organs could first be removed with the assurance that their 

 influence would be shown on the later stages of regeneration could be 

 distinguished after 12 hours by observing the rate at which regeneration 

 was taking place. 



The foregoing data seem to show conclusively that there is a clearly 

 marked influence of the sense-organs upon the rate of regeneration in 

 Cassiopea. There is no evidence, however, that the presence of this 



