134 



REPORTS o? inve;stigations and projects. 



of importance is that the new disk-tissue regenerates rapidly at first and 

 almost completes itself within the first 12 days and then begins to differen- 

 tiate. After this time both groups are growing only the 5 new arms and so 

 decrease about equally in size. The more tissue the animal is regenerating 

 the more rapidly is its old body-size diminished, and it would finally be 

 emaciated and exhausted by this growth. 



The experiment further supplies data bearing upon the influence of the de- 

 gree of injury on the rate of regenerative growth. The first group has a total 

 amount of injury less than that of the second, yet both groups are growing 

 equal numbers of oral-arms. The table below shows the average length in 

 millimeters of the regenerating arm-buds after given periods of time : 



The arms in both groups are regenerating at equal rates, although one 

 group is more injured than the other. The less injured group regenerated 

 faster than the more injured during the early part of the experiment, but this 

 advantage was later lost. This evidence shows, as did my previous results, 

 that the rate of regeneration is not always influenced by the degree of injury. 



A second experiment consisted of 2 groups each of 14 individuals of the 

 same average sizes. These medusae were operated upon so as to remove the 

 stomach and all the mouth-arms from the first group, leaving only the medusa 

 disk, while 5 oral arms and a part of the disk were cut from the other group 

 in a manner exactly similar to the second group of the above experiment. 



The first group regenerates a thin film of tissue to cover the central stomach 

 space. This tissue often tears and reforms several times, then begins to 

 thicken, and finally forms new arm-buds, so that the actual amount of regener- 

 ating tissue during the early period of the experiment is more than in the 

 other group. Accompanying this we find a greater decrease in disk diameter 

 in these specimens during the early part of the experiment. Gradually, 

 however, the two groups come to decrease in size at about equal rates, as 

 indicated in the average measurements shown below : 



Group. 



Group I (arms and 

 stomach off) 



Group 2 (5 arms and 

 disk cut) 



The first group lost 26.6 mm. in diameter during the first 14 days, while 

 the second group lost only 19 mm. From the twenty-second to the twenty- 

 eighth day of the experiment the first group lost 4.4 mm. and the second 

 group 4 mm., about the same in each case. Here again it is shown that while 

 .the medusae are regenerating large amounts of tissue they decrease more 



