102 C. M. CHILD 



turned to water, advanced to the blastula stage during the alco- 

 hol period, but no movement occurred until returned to water. 

 At the end of the alcohol period partial death, ranging from a 

 few apical cells to the apical half had occurred in from 25 to 40 

 per cent. The resulting forms are all without skeleton and show 

 differential inhibition of the more extreme degrees, with apical 

 differential recovery indicated by apical outgrowth, as in figures 

 74 to 81, in 30 to 40 per cent. The remainder, mostly partial 

 basal forms, are spherical with entodermal vesicle (figs. 19 to 

 21) and show no differential recovery. 



Late cleavage stages in 3 per cent alcohol, 18 hours, advance 

 to beginning of gastrulation during this period, but 10 to 20 

 per cent show a small amount of apical death. Resulting forms 

 are from 30 to 40 per cent differentially inhibited plutei with more 

 or less rudimentary skeleton like figures 7, 12, 13, and with no 

 evidence of differential recovery; 30 to 40 per cent are askeletal 

 rounded forms with apical outgrowth like figures 74 to 81; and 

 the remainder are spherical with entodermal vesicle, mostly par- 

 tial basal forms, without differential recovery. This case shows 

 an interesting feature of the relation between differential inhi- 

 bition and differential recovery. Those individuals which are 

 least inhibited develop most rapidly and so attain an early 

 pluteus stage before differential recovery occurs to any great ex- 

 tent. Consequently they show only the lesser degrees of differ- 

 ential inhibition. Those which are more susceptible are more 

 retarded in their development, and even after return to water 

 attain a less advanced stage of development, but, nevertheless, 

 show a greater degree of differential recovery than the less sus- 

 ceptible, because renewed growth and development are limited 

 to the apical region, while in the less susceptible individuals they 

 occur more or less over the whole body. Finally, in the most 

 susceptible individuals, more or less of the apical region is killed, 

 and differential recovery does not occur to any appreciable ex- 

 tent. In short, the forms characteristic of differential recovery 

 can be produced only within certain limits of inhibition. If the 

 degree of inhibition be not sufficient or be too extreme, the de- 

 gree of differential recovery is not sufficient to affect the form of 

 the animal. 



