132 Papers from the Department of Marine Biology. 



mens in sea-water could not be distinguished from the surrounding 

 tissue. Long before this time tissue differentiation had taken place, 

 so that functional nerves, muscles, gland and sensory cells had been 

 formed from the syncitial mass into which the epithelial layers had 

 been converted in the earliest stages of regeneration. 



EXPERIMENTS WITH ENTIRE DISKS. 



When the rates of regeneration of a series of active and inactive entire 

 disks is compared it is found that in about 75 per cent of all the experi- 

 ments the regeneration is most rapid in the active specimens. In the 

 remaining disks the amount regenerated at any given time is (in about 

 10 per cent of the pairs) found to be equal within the limits of accuracy 

 of measurement, while in about 15 per cent of the pairs of disks 

 regeneration was greatest in the inactive specimens. 



The results of many different kinds of experiments upon Cassiopea 

 show wide variations in the sensitivity and metabolic activity in this 

 animal. It therefore seems evident that the conflicting results obtained 

 from specimens subjected to this type of operation are to be explained 

 as individual variations in physiological activity. 



More dependable results may be expected from specimens prepared 

 according to Stockard's method (fig. 3) , where individual variations in 

 physiological activity are eliminated. 



After this operation the inactive half of each specimen is moved 

 about by the pulsation of the active half, so that there can be little 

 difference in the degree of aeration of any two parts of the disk. In all 

 experiments of this type (entire disks with the halves insulated from 

 each other) where large numbers of specimens were used two difficulties 

 were met in making the measurements. Frequently the disk became 

 folded backward at the point where the subumbrella ectoderm was 

 removed, sometimes even bringing the exumbrella surfaces in contact. 

 While this seemed in no way to interfere with regeneration, it frequently 

 made accurate measurements impossible unless the specimen was first 

 narcotized, as any attempt to unfold the active disk usually resulted 

 in tearing the delicate regenerating tissue. This procedure involving 

 the expenditure of so much time, all badly folded specimens were 

 discarded. If the folding took place some days after the start of any 

 series of experiments the specimen was discarded and the figures for 

 the earlier stages were retained in the record. 



The other most common source of difficulty in making the measure- 

 ments arose on account of the tendency of the edge of the regenerating 

 tissue to fuse with the edge of the old cut surface or with a more proxi- 

 mal part of the sheet of regenerating tissue. Whenever the edge of the 

 thin sheet of new tissue became folded back sufficiently to touch any 

 of the more proximal tissues fusion took place, so that a tube would be 

 formed from the new tissue. When the folding involved only a small 



