Factors ni Regeneration 355 



1 Inverting pieces is almost certain to stimulate regeneration 

 at basal ends; or, better still, embed inverted pieces in sand and 

 a remarkable number of basal polyps appear on the free parts. 



2 Tying a ligature at the distal end of a stem or, still better, 

 ligature the lateral branches, then ligate the middle of the stem, 

 and a greatly increased number of heteromorphic polyps result. 



3 By cutting small pieces from any part of the colony a far 

 greater number of polyps is produced at the basal than at the 

 apical ends. 



Thus though the coenosarc is influenced by such external factors 

 as gravity, ligatures, lack of oxygen, cold, and by internal factors, 

 such as age, size of the piece, etc., the ccenosarc normally behaves 

 in certain definite zvays ivhich, without the aid of hypothetical 

 " specific stuffs ' not only accounts for the absence of polyps at cer- 

 tain cut ends but accounts for their regeneration at other ends. Under 

 a given set of conditions %ue can foretell tvith a fair degree of accu- 

 racy the number and region at ivhich regeneration ivill take place. 



Furthermore, it is not necessary to have recourse to the stimu- 

 lating effects of necrotic tissues thrown into the circulation to 

 account for the regeneration of polyps. In Tubularia it has been 

 maintained that the breaking dovv^n of the partition near the cut 

 end throws into the circulation material which stimulates regen- 

 eration at that end. In a hydroid resembling Eudendrium, namely, 

 Pennaria, Gast and Godlewski believed that the disintegration 

 of polyps supplied the circulation with material which stimulates 

 regeneration. In Eudendrium there is neither a partition as in 

 Tubularia, nor were the polyps permitted to disintegrate, for they 

 were cut off at the beginning of the experiment. Yet hydranths 

 were formed within 48 hours often at every cut end. Even when 

 hydranths were daily removed as soon as formed, other polyps 

 were regenerated. 



The following internal factors affect regeneration: 



I Age determines not the kind but the rate and number regen- 

 erated. The younger the region the more numerous and the 

 quicker do polyps appear. This statement is subject to special 

 conditions already enumerated, such as ligatures, inversion of 

 stems, migration of the coenosarc, etc. 



