82 C. M. CHILD 



If this localization is chemotactically determined, as is com- 

 monly believed, then we may say that a certain difference in 

 metabolic rate along the apico-basal axis is necessary as a basis 

 for the differential chemotactic action. 



Attention must be called to the possibility that, in some of the 

 forms shown in figures 40 to 48, the original apical region has 

 been killed before acclimation, and that the apical outgrowth is 

 a reconstitution from more basal regions. It is perfectly cer- 

 tain from the observations on earlier stages that forms like 

 figures 40 to 43 may develop without any apical losses, but it is 

 probable that at least in some cases forms like figures 44, 46 

 have lost some apical cells. In forms such as figures 38, 39, 

 40 to 48, which are very characteristic of acclimation in alcohol, 

 the acclimation involves chiefly the more apical regions of the 

 body, while in the basal regions the effect of inhibition persists. 

 The difference between these forms and the acid forms (fig . 41 

 to 37) is due to the fact that in acids differential acclimation 

 begins earlier in the regions of highest metabolic rate of the 

 various axes and is more complete than in alcohol, therefore the 

 extremes of the resulting form changes are greater than in alco- 

 hol. In alcohol differential acclimation overcompensates the 

 effects of differential inhibition only in the more apical regions 

 of the apico-basal axis, and differential acclimation along the 

 antero-posterior axis plays little or no part in determining the 

 form, while in acids the differential effect is merely greater in the 

 apico-basal axis and is also marked in the antero-posterior and 

 medio-lateral directions. 



The lower limits of differential acclimation are reached in the 

 partial basal forms where a considerable portion of the apical 

 region of the ectoderm has been killed by the direct inhibiting 

 action of the agent. Without acclimation, such forms remain 

 spherical, the blastopore usually closes and the entoderm be- 

 comes a closed vesicle in the blastocoel (figs. 19 to 21), but, un- 

 der conditions which permit some degree of acclimation, they 

 give rise to forms like figures 49 to 53. In these a small apical 

 outgrowth may occur with the mouth at its base, presumably 

 on its anterior side (fig. 49) ; the mouth may lie at the apex of 



