CERTAIN GENERAL CHARACTERISTICS 



37 



nance decreases. In pieces of equal length from different stem-levels rate 

 of hydranth development decreases at both ends of the piece with increas- 

 ing distance of the level of reconstitution from the oral end of the stem, 

 but in extreme proximal regions the differences may be slight or absent. 

 Although all earlier investigators who concerned themselves with the 

 question of rate at different levels of the Tubularia stem were essentially 

 agreed as to the presence of these differences, Garcia-Banus (1918) pre- 

 sented experimental data to show that they do not exist. Hyman (19206), 

 however, showed conclusively that they are present in animals in good 

 condition and pointed out that the rates recorded by Garcia-Banus were 

 so much lower than others had found them that his material could not 

 have been in a condition comparable to that used by others. Hyman's 



data for oral hydranths on distal and proximal halves of the same stems 

 are given in Table i. 



In a more recent study Barth (1938a), taking volume of hydranth 

 primordium divided by time from section to emergence of hydranth 

 {irr^L/t) as the measure of rate of reconstitution, obtains much greater 

 difference in rate at different stem-levels, since stem diameter and length 

 of hydranth primordium decrease and length of time from section to emer- 

 gence increases from distal to proximal levels. It seems open to question 

 whether volume of hydranth primordium should be employed in a measure 

 of rate in this case. Diameter of the primordium depends on diameter of 

 the stem, which has nothing to do with reconstitution; and length of the 

 primordium is not the result of growth but depends on the gradient length 

 and scale of organization determined a few hours after section, before the 

 primordium becomes visible (see pp. 101-2). Neither diameter nor length 

 has anything to do with cell formation or growth; consequently their rela- 

 tion to rate of reconstitution appears at least doubtful. Driesch (18996), 



