2 MARIE A. HIXRICHS. 



acclimate or recover. (See Child, '24^, p. 247, for review of 

 literature.) 



Differential inhibition and differential recovery have been 

 brought about (i) through the use of visible radiation (diffuse 

 daylight, direct sunlight filtered through a glass dish containing 

 water an inch deep, artificial light from two i,5OO-watt photo- 

 graphic bulbs, and from the white-flame carbon arc) plus the 

 action of the following sensitizing dyes: eosin, neutral red, 

 benzoflavine, and methylene blue; and (2) by means of radiation 

 from a mercury-vapor arc. (See also Child, '246, footnote, 

 p. 109.) Differential acclimation has been brought about by 

 continuous exposure of sensitized eggs to diffuse daylight. 



The development of eggs of Echinoderms has been repeatedly 

 modified experimentally, 1 but the fact that there are relative 

 differences in degree of susceptibility to modification of the 

 various regions along the embryonic axes has not been generally 

 noted. (For a more complete discussion of the results obtained 

 by differentially modifying development, see Child, '16 and '23.) 

 The main conclusions reached by this author regarding the forms 

 attained in this way may be summed up as follows : 



1. "In cases of differential inhibition the chief changes are 

 decrease in size of oral lobe, w r hich represents the apical region, 

 decrease to zero in the angle of divergence between arms, ap- 

 proach of lateral parts toward the median line and in more 

 extreme degrees fusion in the median line, the progressive 

 obliteration of antero-posterior and medio-lateral differences and 

 finally of apico-basal differences. 



2. "The changes in differential acclimation and differential 

 recovery are in the opposite direction. They consist in increase 

 in size and over-development of the oral lobe, increase to 180 

 in the angle of divergence between the arms, and over-develop- 

 ment of anterior and median as compared with posterior and 

 lateral regions. 



1 For literature on modification of development see the following; 



(A) Visible radiation following sensitization Cooke and Loeb, '08, "09. 



Shippen, '07. and Loeb, '07, a, b. 



(B) Ultraviolet radiation Baldwin, '15, Stevens, '09, Ruppcrt, '24, Child, 



'246, footnote, p. 109, Clarke, '22. 



(C) X-rays and radium Loeb, '22, Colwell ami KIKS. '.'4. Hinruhs, '25 



(unpublished). 



