Factors m Regeneration 341 



basal and almost //// lateral regeneration. Furthermore, the total 

 number produced varies with the amount of free coenosarc (not 

 embedded in sand). 



EFFECTS OF CONTACT^* 



Experiment 16. Stems were suspended on two horizontal 

 threads, others were in contact with the bottom of the dish. Hy- 

 dranths appeared on the two series at the same time. 



This experiment agrees with No. 13, in that stems surrounded 

 by water and otherwise under identical conditions produce a 

 larger number of polyps than those in contact with a solid body. 



Experiment ly. Shallow V-shaped grooves were made in a 

 cake of paraffin of such a width that when stemswere placed therein 

 the lateral branches were in contact with the sides or bottom of 

 the grooves. A record of each lateral end was made, whether (a) 

 it pointed upward and out of the groove and therefore not in con- 

 tact with the paraffin, {h) it extended sideways and touched the 

 sides of the groove, (c) it pointed downward, and therefore in con- 

 tact with sides or bottom of the groove. In six days only 23 per 

 cent of all the ends regenerated polyps. Further details will more 

 clearly illustrate to what degree contact suppresses hydranth for- 

 mation. During the first six days but 7 per cent of all downward 

 pointing branches (in contact), 8 per cent of all sideways pointing 

 branches (in contact), 43 per cent of all upward pointing branches 

 (free) regenerated polyps. Two hundred and thirty-six branches 

 were used in this experiment. 



Experiment 18. Stems were put within glass tubes, i to l^ mm. 

 inside diameter. One or both apices of some stems extended beyond 

 the tube, in others several branches protruded beyond the tube, 

 or short glass rings were so arranged that some of the lateral 

 branches were free between the rings. In nearly every instance 



^''Some hydroids react more quickly and more readily to contact than do other hydroids, Campan- 

 >ularia and Pennaria more than Eudendrium. See Loeb '91. 



