AN ATTEMPT TO ANALYZE THE PHENOMENA OF 

 POLARITY IN TUBULARIA. 



BY 



T. H. MORGAN. 



Two questions arise in connection with the problem of polarity 

 in Tubularia: (l) The kind of structure, polyp or stolon, that 

 develops on a cut surface; and (2) the time at which the new 

 structure appears. The former includes the idea of "polarity" 

 in the usual sense; but, as I shall attempt to show, the time of 

 appearance of the new structure may also be an important factor 

 in determining the kind of structure that develops when an alter- 

 native exists. 



A cut surface at any level may produce a polyp or a stolon. 

 Usually polyps appear on distal cut surfaces, stolons on basal 

 ones. An external stimulus, viz: exposure of a cut end to water, 

 calls forth the development of a hydranth and the hydranth may 

 develop either on a distal or on a basal surface. If a piece is 

 open at both ends, the oral hydranth develops first, and after it 

 has emerged, the aboral end may also produce a polyp, rather 

 infrequently in Tubularia marina, but more often in T. mesem- 

 bryanthe?nuf?i and T. crocea. On the other hand, if the stem 

 is tied in the middle, the basal polyp develops sooner than when 

 the stem is not tied, and it appears in practically every instance. 

 The aboral development takes place to a large extent independently 

 of the length of the stem between the ligature and the aboral end. 



How can we account for these facts ? We can at least formulate 

 a provisional hypothesis. We may assume that the gradation of 

 the material is of such a kind that the hydranth-forming material 

 decreases from the apical toward the basal end. The formative 

 influence, acting from the exposed end inward (the stimulus of 

 the water on the free end), finds a prompter response when it 

 acts in the direction of decreasing amounts of hydranth-forming 



