THE RANGE OF DOMINANCE 135 



sea-water to a certain extent the metabolic rate in pieces 

 is increased, and under these conditions pieces which 

 in normal sea-water produce only hydranths at their 

 basal as well as apical ends produce in a large percentage 

 of the cases stolons which later develop hydranths at their 

 tips/ The hydranths in such pieces are longer and 

 larger than in normal sea-water. 



When a piece is cut with a fully developed active 

 hydranth at its apical end, no hydranth appears at the 

 basal end until the metabolic rate of the apical hydranth 

 decreases or its death occurs, which in Tubularia is 

 usually within a few days at most. In Corymorpha 

 relations are similar. Evidently, then, a full-grown, 

 active, apical hydranth inhibits the development of a 

 basal hydranth in a piece, but a hydranth beginning to 

 develop at the apical end is usually only able to retard 

 to some extent the development of the basal hydranth. 

 The dominance of the full-grown hydranth is more 

 effective than that of the early stages of hydranth 

 development. 



Various investigators have observed that when the 

 development of the hydranth at the apical end of a piece 

 is inhibited by inclosing this end in paraffin or sticking 

 it in the sand the development of the hydranth at the 

 basal end is accelerated, and it has been found that in 

 such cases the basal hydranth is longer and larger than 

 when the apical hydranth is not inhibited. Evidently 

 the inhibition of development at the apical end decreases 

 dominance, and the establishment of the new gradient 

 and so the development of a hydranth at the basal end 



^ Child, ''An Analysis of Form Regulation in Tubularia. I," 

 Archiv fur Entwickelungsmechanik, XXIII, 1907. 



