Rate of Regeneration in Cassio/>ea .vaniaeluina. 81 



portion of the disk, while the latter does not pulsate until a sufficient ritn 

 of new tissue has formed around its cut edge, usually requiring about two 

 days after the operation. Yet the rate of regeneration is practically the 

 same from corresponding parts of the two pieces. The physical condition 

 of the strip and center piece must be closely similar, since they are parts 

 of the same individual. It is important to remember here that the sense- 

 organs and a part of the nerve-ring accompany the strip, while the central 

 part has much less nervous tissue ; yet this fact seems to cause no difference 

 in the rate of regeneration of new tissue from the two pieces. The question 

 of the influence of activity and rest will be attacked in a more conclusive 

 manner in the next section. 



REGENERATION DURING ACTIVITY AND REST- WITH AND WITHOUT 

 RHYTHMICAL CONTRACTIONS. 



Zeleny has suggested, with reservation, that when several appendages 

 are removed, the effort to use the regenerating ones, or exercise, may cause 

 the buds to grow faster. The general question of the influence of the 

 nervous system on regeneration is an important one. Since Cassiopea is 

 an animal with a rhytlmiically pulsating movement, it seemed likely that an 

 experiment might be so arranged as to test the influences of activity and 

 rest on the rate of regeneration. With such an idea in view a number of 

 experiments were performed, the most satisfactory being recorded below. 



A ring about 20 mm. in width was cut from the margin of the disk. 

 The sense-organs were removed from half the periphery of this ring, while 

 equal-sized pieces of tissue between the sense-organs were cut from the 

 other half, the degree of injury thus being practically equal on the two halves. 

 If, then, the epithelium was scraped across between the sense-organ half 

 and the other without sense-organs, the first half continued to pulsate, while 

 the latter comes to rest (see fig. 28, a). Such a ring will regenerate tissue 

 toward the center until the circular space is covered over. Careful measure- 

 ments were made on six preparations of this kind with two controls which 

 had the entire ring in motion and two others with all the ring at rest. 

 Comparing all measurements, it seems as though the tissue was regenerated 

 at approximately equal rates from the two halves (fig. 28. b). From this 

 e.xperiment one is unable to find any reason to believe that activity or effort 

 is capable of accelerating the regeneration rate. In this animal the rate of 

 regeneration seems to be independent of the nervous impulse necessary for 

 activity. The experiments given in the previous section, as well as those 

 to be considered in connection with the influences of various salt solutions 

 on the rate of regeneration, also furnish some evidence on the question of 

 activity and rest as determining factors. 



Child (1904) has, in a number of contributions upon the subject of Reg- 

 ulation, held that activity exerts a marked influence upon the manner of 

 regeneration. He has also claimed that the nervous svstem exerts an in- 



6 



