Studies of Tissue Growth 437 



which arises when several individuals are compared is in this way 

 eliminated. 



Fifteen medusae 90 mm. in disk diameter were divided, May 21, 

 into three groups of five each. Fifteen others each 105 mm. in 

 diameter were similarly grouped and the three groups prepared 

 as above described. 



Two days later, May 23, the average growth from each group 

 was 3 mm. in width. After four days the tissue averaged about 

 7 mm. in width in each group, the central spaces being almost 

 covered over. The preparations with one-half in motion and 

 one-half at rest had equally wide bands of tissue growing from the 

 two halves. In almost all cases, however, there was a slight 

 indentation in the new tissue just over the place where the insula- 

 tion was made by scraping the epithelium between the two halves 



(Fig- 3)- \ 



Comparing the average amounts and rates of regeneration in 



these three classes of preparations it is found that" tissue grows 

 from the circular cut to cover the disc center at equal rates from 

 the rings in motion, the rings at rest, and the rings with one-half 

 in motion and the other half at rest. There is no influence due 

 to functional activity on the rate of regeneration in Cassiopea. 

 It follows, therefore, that the eff^ort to use an organ or the more 

 urgent need of it probably does not cause its more rapid re-for- 

 mation. 



Zeleny has also performed experiments on Cassiopea to test 

 the influence of functional activity on the rate of regeneration. 

 His experiments difi^er from mine in that all comparisons were 

 made between diff"erent individuals and that he established in the 

 specimens a rhythmical pulsation which generally ceased before 

 the close of the experiment. In my work the normal periodic 

 pulsation of the disk was utilized and it, of course, persisted 

 throughout the experiment. Although Zeleny used only a few 

 individuals his results agree with mine in that he finds the speci- 

 mens at rest to regenerate tissue equally as rapidly as do those in 

 action. In some of his cases the resting specimen had a slight 

 advantage over the one in motion, although this may easily have 

 been due to individual difi^erences since such a source of error is 

 not sufl&ciently controlled. 



