186 C. M. CHILD. 



of the stolon is usually inhibited or retarded until the hydranth- 

 stem axis attains sufficient length to permit some degree of 

 physiological isolation of the stolon tip. Often the stolon serves 

 as nutritive material for the developing hydranth and stem and 

 may be completely resorbed. Fig. 19 shows a case in which such 

 resorption is going on. The stolon, originally filling the perisarc, 

 is much reduced and irregular in outline, while in the hydranth- 

 stern axis the coenosarc fills the perisarc. Moreover, the stolon 

 coenosarc, particularly in the most reduced regions, is almost 

 transparent, while that of the hydranth-stem axis appears more 

 granular and denser. By means of inhibiting conditions these 

 hydranth-stem axes may be again transformed into stolon axes or 

 inhibited to such an extent that they serve as material for the 

 growth of stolon axes and are resorbed. With the approach of 

 exhaustion also, the hydranth-stem axes usually undergo resorp- 

 tion, while the stolon axes persist and grow, at least for some days 

 longer. 



THE APPEARANCE OF NEW POLARITIES. 



As noted above, the spherical, apparently completely apolar 

 forms undergo no further development unless some degree of 

 acclimation or recovery occurs and then they apparently develop 

 new polarities. Occasionally in cases of rapid recovery a 

 hydranth-stem axis arises directly from the upper free surface of 

 the flattened mass (Fig. 22). In the absence of landmarks the 

 possibility cannot be absolutely excluded that this outgrowth 

 represents the hydranth-stem axis of normal development. On 

 the other hand, observation indicates that the spherical forms 

 may come to rest with any part of their surface in contact and that 

 their polarity has been completely obliterated. If this is true, 

 the hydranth-stem axis developing from the upper surface 

 represents a new polarity determined by differential exposure of 

 free surface and surface in contact, probably involving differences 

 in intake of oxygen or the giving off of COa or both. 



Figure 23 shows in side view a case of simultaneous develop- 

 ment of two axes from a spherical apolar form. The axis arising 

 from the upper surface is a hydranth-stem axis, that from the 

 side, a stolon* axis. Since these axes develop from a spherical, 

 apparently apolar form, it seems probable that both represent 



