Rate of Regeneration in Cassiopca xamaehana. 69 



to appear after 23 days. The disk had resumed its rythmical pulsation in 2 

 days after the operation. It will be found by a study of the table that after 

 about 12 days the regenerated tissue began to decrease in width. This fact 

 may be explained by the thickening which the new tissue commences to 

 undergo at this time, or again it may result from the causes which tend to 

 make the entire disk gradually decrease in diameter, until after 35 days it 

 is little more than half as large as it was when the experiment began. 



Nos. 4 and 4A were cut so that only the center of the disk covering the 

 bases of the mouth-arms remained. From Xo. 4 a strip almost one-third 

 as wide as the entire diameter of the medusa was cut away. This disk 

 was 90 mm. in diameter before the operation and only 34 mm. after the 

 removal of the strip. It must also be kept in mind that the cut surface at 

 this level is very thick, since the disk is thickest at the center and becomes 

 thinner as the margin is approached. No. 4 died soon after the experiment 

 started, as is indicated in the table. No. 4.\ was healthy and within 6 days 

 had regenerated a rim of tissue from its cut surface which was almost twice 

 as wide as that observetl in any of the above experiments. After 12 days, 

 here again, the regenerated strip ceased to increase in width, but continued 

 to become thicker. Finally, as is shown in table I, the rim of new tissue 

 actually began to decrease in width as it had in 3.\. 



The deep-cut surfaces when regenerating first grow a wide, thin rim of 

 tissue which finally begins to thicken at the expense of radial growth till 

 the normal thickness of the disk at the given level is reestablished. It will 

 be seen that regenerating tissue from a cut surface near the disk margin 

 widens slowly, but almost continuously, as at this level the disk substance is 

 very thin and no subsequent thickening of the regenerated tissue is necessary. 



Three medusae were now cut so that in two individuals only a small bit 

 of disk remained attached to the mouth-arms and in the third the entire 

 disk was removed. The object of such operations was to ascertain whether 

 the mouth-arms were able to regenerate a disk, or disk-tissue. It was found 

 that the very small portions of the disks which remained would regenerate 

 new tissue, but the mouth-arms were incapable of regenerating from their 

 bases, although they healed the wounded surfaces and lived for 29 days 

 after the entire disk had been removed. 



Other experiments on removing strips of various widths from the periph- 

 ery were made and results closely similar to those above were obtained. 

 One must then conclude that the disk of Cassiopea begins to regenerate its 

 margin at a faster rate the nearer the cut is to the center of the disk. A 

 small individual regenerates proportionately faster than a large one. These 

 results are closely similar to those obtained by Morgan on the salamander, 

 fish, and earthworm, and by comparison show- that the rates of regeneration 

 differ at different levels of the body, and further that (as in embryonic 

 growth t the nearer the normal body-size or form is approached the slow'er 



