Q2 MARY GRACE SPRINGER. 



development, as, for example, the variations of the angle of diver- 

 gence between the arms, the approach of the lateral parts to the 

 median line, and in extreme cases fusion, and many differences in 

 the proportions of the larvae. 



Child also endeavored to show that differential acclimation and 

 recovery may take place, resulting in wide-angled plutei, and an 

 increase in the size of the oral lobe with over-development of the 

 anterior and median regions as compared with the posterior and 

 lateral regions. No specificity in the different form changes pro- 

 duced by the different agents used was noted. 



In the experiments described here, also, the deviations from the 

 normal form of the embryos produced by the extracts were so 

 varied that there seems to be no basis for claiming any specificity 

 of action. All the evidence points not toward a qualitative, but 

 a quantitative action of the extract as far as the normal processes 

 of growth and development are involved. 



Although it is impossible at this point to state whether or not 

 the different extracts all produce the same effect on the developing 

 Arbacia egg, the fact which is to be emphasized is that, however 

 they act, or whatever processes of the egg are chiefly involved, the 

 general effect of the extracts when present in sufficient concen- 

 trations is to retard or inhibit the fundamental metabolic processes 

 in some way. 



There is a definite normal rate of development for the eggs of 

 each animal, yet this rate may be changed by various conditions of 

 environment. The two most common modifying causes are a 

 change in oxidation (which may be due to a variety of causes) and 

 a change in temperature. Among others, Stockard 20 has shown 

 recently in many experiments that a very wide range in the de- 

 crease of developmental rate is very easily brought about by even 

 a slight change in the surrounding temperature or a reduction 

 in the oxygen supply. He has also contended that a normal con- 

 tinuous development may be modified into a discontinuous one by 

 stopping its course during a very early stage. 



Now many variations from the normal were found to be pro- 

 duced by the use of the extracts in certain concentrations. Some 



to 



Stockard, C. R., " Developmental Rate and Structural Expression," Amer. 

 Journ. of Anat., Vol. XXVIII., No. 2, January 15, 1921. 



