THE AXIAL GRADIENTS IN HYDROZOA. 



2. Stolon formation can be induced at all levels of the stock. 

 The stolons may arise as adventitious outgrowths, by transfor- 

 mation of hydranth buds, or by transformation of terminal re- 

 gions of stems after disintegration or resorption of hydranths. 



3. These facts, together with data concerning the physiologi- 

 cal gradients in hydroids indicate that the stolon axis is a some- 

 what inhibited gradient and less "steep" than the hydranth - 

 stem gradient. The separation of stolons from the stock and the 

 continued growth of stolon tips at the expense of lower levels in 

 the absence of food are regarded as necessary consequences of 

 the presence in the stolon of an axial gradient. 



REFERENCES. 

 Child, C. M. 



'15 Individuality in Organisms. Chicago. 



'19 The Axial Gradients in Hydrozoa. II. BIOL. BULL., XXXVII. 



'21 The Axial Gradients in Hydrozoa. IV. BIOL. BULL., XLI. 

 Hyman, L. H. 



'20 The Axial Gradients in Hydrozoa. III. BIOL. BULL., XXXVIII. 

 Loeb, J. 



"92 Untersuchungen zur physiologischen Morphologie der Tiere. II. Wiiizburg. 



'oo On the Transformation and Regeneration of Organs. Amer. Jour. Physiol., 



IV. 

 Lund, E. J. 



'21 Control of Organic Polarity by the Electric Current. I. Jour. Exp. Zoo!., 



XXXIV. 

 Morgan, T. H. 



'01 The Factors that Determine Regeneration in Ant annular ia, BIOL. BULL., II. 

 Peebles, Florence. 



'oo Experiments in Regeneration and in Grafting of Hydrozoa. Arch. f. 

 Entwickelungsmech., X. 



'02 Further Experiments in Regeneration and Grafting of Hydroids. Arch. f. 



Entwickelungsmech., XIV. 

 Stevens, N. M. 



'02 Regeneration in Anlennularia ramosa. Arch. f. Entwickelungsmech., XV. 



'10 Regeneration in Antennularia. Arch. f. Entwickelungsmech., XXX. 

 Thacher, H. F. 



'03 Absorption of the Hydranth in Hydroid Polyp?. BIOL. BULL., V. 



