6 LEWIS R. GARY 



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 Hmits 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 Cassi- 

 opea have shown that there are wide variations in the sensitivity 

 and metabolic activity in this animal. It therefore seems evi- 



Fig. 3 To illustrate the type of operation (Stockard's) used in experiments 

 of types 3 and 4. The sense organs were removed from one-half of the disk, and 

 an equal amount of tissue from the margin between the sense organs of the other 

 half of the disk. The two halves were then insulated by scraping off two diamet- 

 rically oi)posite strips of subumbrella ectoderm. The insulatingstrips are shown 

 stippled in the figure. 



dent that the conflicting results obtained from specimens sub- 

 jected 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 (2) where large numbers 



