THEORY OF AXIAL GRADIENTS 



269 



TABLE 2 



Time in hours required for the emergence of the oral hydranths of three pieces of 



equal length, from the same stem of Tubularia 



Length of the pieces = 10 mm. 



the oral hydranths were in hours : for the apical piece 92, for the 

 middle piece 84, and for the basal piece 76. We have chosen 

 the experiment, the results of which are given in table 2, as an 

 example, because in it the individual differences are not very 

 great, so that the data are more constant and the averages more 

 reliable. It is therefore a mere matter of chance whether the 

 oral hydranths of the apical or basal pieces emerge first, as long 

 as both pieces have equal length. 



Comparing pieces of different size from the same stem. Child 

 found that the shorter pieces will form hydranths a little later 

 than the longer ones, but he states that since the more basal 

 pieces will form the oral hydranths later than the more apical, 

 the pieces must be cut in such a way that the shorter piece is 

 always the more apical one. Thus he says the two factors of size 

 and level are opposed to each other instead of acting in the same 



