LOCALIZATION OF NEW AXES IN CORYMORPHA. 479 



gated, but it is difficult to believe that the localization begins in- 

 dependently of external factors of some sort which determine 

 where the first tentacle or tentacles shall appear. In the ordinary 

 course of reconstitution the entodermal canals are important fac- 

 tors in localizing the new tentacles, as Torrey has shown ( Torrey, 

 '10). Factors concerned in tentacle localization in the lateral 

 polarities have not been studied, but they will probably be found 

 in the relations of the growing region to the rest of the stem. 

 Study of Hydra and various hydroids indicates that localization 

 of a single tentacle is sufficient to initiate the orderly development 

 of others. Torrey's study of the order of appearance of tentacles 

 in the embryonic development of Corymorpha is interesting in 

 this connection as indicating that different localizing factors are 

 concerned in different individuals for he finds that the process does 

 not follow a uniform course (Torrey, '07). Apparently each 

 region of growth, whether tentacle or other organ, dominates a 

 certain area so that a similar organ cannot develop within that 

 area. When a particular tentacle is localized, for example, an- 

 other can develop only outside its range of dominance. Any part 

 of the circumference in the tentacle forming region is undoubtedly 

 capable of giving rise to a tentacle, but the actual localization in 

 a particular case must depend on the factors concerned. That 

 the outgrowth which becomes a polar axis with a radial symmetry 

 can localize its own tentacles independently of any of the external 

 differentials to which it is exposed is at least highly improbable 

 and seems to require the action of some non-mechanistic ordering 

 factor. If these observations and suggestions are correct, radial 

 symmetry in these new axes has its origin in the primary likeness 

 of radii at any particular level and in the difference between sur- 

 face and interior which is present in some form in all organisms. 

 The later localization of a series of similar organs in radial ar- 

 rangement seems to demand the action of some differential external 

 to the parts concerned. 



SUMMARY. 



i. Buds have never been seen to arise from lateral stem regions 

 in CorymorpJia and a simple transverse cut into the side of the 

 stem closes rapidly without development of a bud or other out- 

 growth, unless it extends almost through the stem. 



