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Experiments with Entire Disks

tissue, regeneration, disk, active and sheet


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 remkining 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 m eask 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 area separation could be easily accomplished, but if a considerable portion of the regenerating sheet was involved the specimen was rendered useless for further study.

The results of two typical experiments are shown in table 1. The measurements are in millimeters. The upper figure for each date shows the width of the sheet of tissue regenerated from the active half disk, the lower figure the width of that regenerated from the inactive half-disk. When the sheet of new tissue had entirely closed over the

cavity in the center of the disk the point of closure remained recogniz able for at least a day, so that the measurements could readily be made for those disks that had become closed since the time of the last meas urements. By the end of 24 hours after the new sheet of tissue was completed the point of closure would be shifted until it came to lie in the center of the disk.

On the Nervous System of Castricrpea Xamachana. 135 The results from the 40 disks recorded in table 1 are shown in figure 6, in which the divisions along the abscissa show the time of regenera tion in days, those along ordinate the amount of regeneration measured in millimeters. The record for each specimen is carried to the time of closure of the open circle in the center of the disk by the sheet of regenerated tissue.

From the start of regenera- 9 tion the new tissue produced from the side with its sense organs intact is shown to be 8 more rapid. In the early stage of regeneration this difference is more striking 7 upon a cursory examination than in the later stages, al though the actual difference 6 on the rate of growth of new tissue changes only slightly during the entire 5 period of regeneration. The proportion between the amounts of new tissue 4 formed each day, taking the amount regenerated from the side without sense- 3 organs as the unit, was re spectively: First day 1 :1.53 ; second day 1: 1.44; third 2 day 1 : 1.41; fourth day 1:1.38; fifth day 1:1.39.

The regeneration from the half without sense-organs is more regular, as is shown by the fact that for the mean of each day's observation the probable error is less for that half than for the one upon which the sense-organs remain. This result would be expected to follow from the fact that the inactive side was relieved from the influence of the marginal sense organs, which would introduce many stimuli of varying intensity, all of which would have either a retarding or accelerating influence upon the processes of regeneration.

When the rates of regeneration of certain disks in table 1 are com pared with one another, the cause of the uncertainty of the results obtained in experiments with entire disks is clearly shown. The 0 Flo. 8.-Showing relative rates of regeneration of the halves of 40 disks. The upper line represents the half-disks with sense-organs, the lower line represents those without sense-organs.

closure of the open circle in disk 36, table 1, was complete in 2 days, while 5 days were necessary to complete the closure in specimen 30, table 1. Had the latter been the active disk and the former the in active disk of a pair compared in an experiment with entire disks, the conclusion that an inactive disk sometimes regenerates more rapidly than an active one could not have been-avoided.