100 C. M. CHILD 



acclimation. The remainder show various degrees of differential 

 inhibition, the least inhibited being small plutei like figures 12 

 and 13. The various differential inhibitions are of the same 

 types throughout as those produced by KCN, and no forms of 

 any other sort appear in such cases. 



Sodium hydrate 



NaOH is much less toxic than NH 4 OH. Concentrations 

 above ra/500, acting continuously from the first cleavage, usualh^ 

 inhibit development or kill completely at the blastula stage. In 

 ra/500 from the first cleavage, a considerable percentage of total 

 deaths occurs at or before the blastula, and most individuals 

 show more or less apical death. The resulting forms show dif- 

 ferential inhibition, usually of the more extreme types, and 

 many remain spherical basal forms like figures 19 to 21. 



In ra/1000 from the first cleavage, more or less apical partial 

 death may occur in 10 to 40 per cent, but few or no total deaths. 

 Of the resulting forms the majority show some degree of differ- 

 ential inhibition, but some are normal plutei, and some show a 

 slight degree of differential acclimation. All degrees of differ- 

 ential inhibition occur, and differential acclimation appears 

 only in the relatively large oral lobes and wide angles of diverg- 

 ence in some plutei (figs. 23, 24, 29). 



In m 2000 from the first cleavage, apical partial death may be 

 almost entirely absent, or it may occur in 15 to 20 per cent of 

 the blastulae and ranges from the death of a few apical cells to 

 death of about the apical half. A few of the partial basal 

 forms, in which apical death has proceeded farthest remain 

 spherical (figs. 19 to 21) or show some apical reconstitution, 

 but the great majority of the embryos form plutei, almost all 

 of which show the relatively large oral lobe characteristic of dif- 

 ferential acclimation, and in 5 to 10 per cent the angles of 

 divergence are wider than normal (figs. 23, 24, 29). 



In ra/5000 from the first cleavage, the effect on both rate of 

 development and on form is slight. Apical death does not occur, 

 and all form plutei which are either normal or possess a slightly 

 larger oral lobe and slightly wider angles than normal. 



