APPENDIXES 733 



embryonic and larval stages of echinoderms and for planarians and more or less trans- 

 parent oligochetes. The method, properly used, is extremely delicate and of great 

 value as a means of making directly visible certain characteristics of developmental 

 pattern in intact embryos and larval stages of small size, as well as many larger de- 

 velopmental stages. It also serves to show an oxidation-reduction pattern in the ecto- 

 plasm of ciliate protozoa and in adult individuals of many metazoa. In order to avoid 

 misleading results, however, it is necessary to use a wide range of concentrations and 

 staining periods; only in this way is it possible to make certain that an observed differ- 

 ential or absence of a differential is not due to differential toxic action of the dye and 

 consequent retardation of reduction in the injured regions (see pp. 67-70; also Child, 

 i936<7, b). 



