388 LIBBIE H. HYMAN. 



an affirmative answer may be returned. It is possible to modify 

 or eliminate the regional differences in question. The various 

 methods by means of which this was attempted or accomplished 

 are discussed in this section. 



1. The Effect of Cold. A number of experiments were per- 

 formed in which both apical and basal pieces were exposed to a 

 lowered temperature for a number of hours after cutting or 

 during the entire period of regeneration. The pieces were 

 removed from room temperatures (approximately 20 C.) to the 

 temperature of the refrigerator (13 C.) for various periods of 

 time. Although such a proceeding invariably retards the rate 

 of regeneration, the differences between the regeneration of apical 

 and basal pieces were unaltered by such exposure to low tempera- 

 ture. These experiments are therefore included in Table III. 

 (exps. 6, n, 15, 1 6, and 21), as showing the typical difference 

 between the rate of regeneration of apical and basal halves. 

 It is highly probable, however, that with very low temperatures, 

 in the neighborhood of zero, the typical difference between pieces 

 of different level would be reduced or eliminated. 



2. Effect of Using Material Kept in the Laboratory. Two 

 experiments were performed in June upon material which had 

 been kept in the laboratory aquaria for a week preceding the 

 cutting of the pieces. As is well known under such circum- 

 stances, the hydranths of Tubularia fall from the stems and new 

 hydranths are subsequently regenerated. Such new hydranths 

 are smaller than and have a lower rate of activity than the original 

 hydranths; it is therefore to be expected that the regional 

 differences along the axis will be reduced in such cases. As 

 already stated only two experiments were performed as the 

 weather had become warm and little material was available. 

 The material for these experiments was collected on June 30 

 and cut on July 6. The pieces were kept in the refrigerator 

 (13 C.) throughout the regeneration period. The results are 

 given in Table VII. Experiment 21, Table III., furnishes a 

 control for these experiments. It will readily be seen that the 

 differences between the rate of regeneration of apical and basal 

 pieces are plainly reduced as a consequence of the depressing 

 effect of laboratory conditions upon the physiological axis of 



