436 



Charles R. Stockard 



that I determined to repeat my former experiments on a somewhat 

 more extended scale. 



The experiments consisted of three sets of equal sized individ- 

 uals operated upon as follows. With the central point of the disk 

 as a center a circular mass of tissue was removed leaving a pulsat- 

 ing ring of tissue with its outer periphery parallel to the inner cut 

 circle, therefore, all parts of the inner cut are at similar levels 

 (Fig. i) Some medusae had the sense organs removed from the 

 periphery so that the entire ring ceased to pulsate (Fig. 2). Other 



Fig. 1 Fig. 2 Fig. 3 



Fig. I A medusa disk with the center cut away. The ring pulsates and regenerates new tissue to 

 cover the central space. SO, sense organs. 



Fig. 2 A similar preparation with the sense organs removed and in a state of inactivity. The central 

 space is covered equally fast by regenerating tissue. 



Fig. 3 A ring-preparation with one-half active and the other half inactive. Tissue is regenerated 

 equally fast from the two halves. The new tissue is stippled in all of the figures. 



individuals had the sense organs cut from one-half of the periphery 

 and equal sized pieces of tissue from the other half so as to make 

 the extent of injury equal, the half without sense organs was then 

 insulated from the stimulus of the other half by scraping off the 

 oral epithelium between them (Fig. 3). One-half of the prepara- 

 tion now pulsates normally and the other remains at rest. Care 

 was taken to prevent the scraped epithelium from regenerating 

 between the two halves and so reestablishing the pulsation in the 

 quiet half. The conditions in the two halves are as near as pos- 

 sible identical and permit of free comparisons since we are con- 

 sidering two similar parts of one individual which differ only as 

 the experiment provides. The error due to individual differences 



