LARVAL DEVELOPMENT IN THE SEA URCHIN 101 



NaOH in sufficiently high concentration evidently retards or 

 inhibits development and produces all degrees of differential 

 inhibition in form. Differential acclimation occurs more rap- 

 idly and to a greater extent than in NH 4 OH, but still is not 

 sufficient to produce the more extreme types of form character- 

 istic of differential acclimation in alcohol and acids. 



Alcohol 



Development from the first cleavage in alcohol 4 per cent is 

 greatly retarded, and apical death begins at or before the blas- 

 tula stage, usually resulting in total death before or in the gas- 

 trula stage, but in a small percentage more or less of the basal 

 region may remain alive in some lots and a few small spherical, 

 partial forms like figures 20 and 21 may result. 



In alcohol 3 per cent from the first cleavage, total death occurs 

 in 20 to 50 per cent in the blastula or gastrula stage, and most of 

 the others show more or less apical death. The resulting forms 

 show the more extreme types of differential inhibition, and 

 mostly remain without a skeleton. 



Development is retarded in 2 per cent alcohol, but there is 

 usually no death, and differential acclimation begins with apical 

 outgrowth as early as the gastrula stage (figs. 25, 26), and the final 

 stages reached are forms like figures 40 to 48, without skeleton 

 and with an elongated apical outgrowth representing the oral 

 lobe, with a few like figures 49 to 53, which represent partial 

 basal forms. 



In 1.5 per cent alcohol development is less retarded and the 

 degree of differential acclimation is greater. About half the re- 

 sulting forms show marked elongation and over-development of 

 the oral lobe like figures 27, 28, 38, 39, and the remainder range 

 through the forms of figures 40 to 48. 



In 1 per cent alcohol plutei develop which range in form from 

 slight degrees of differential inhibition to slight degrees of differ- 

 ential acclimation, and in lower concentrations there is usually no 

 effect on form. 



A few experiments on recovery after the temporary action of 

 alcohol indicate the possibilities in this direction. Late cleav- 

 age stages in alcohol 4 per cent 11 hours, then washed and re- 



