66 LIBBIE H. HYMAN. 



of developing eggs of Fundulus heteroclitus increase up to the 

 time when the germ ring is at the equator of the egg. Subse- 

 quently they decrease relative to the amount of protoplasm but 

 show an absolute increase owing to the heart beat and other 

 activity. This period when the respiratory metabolism is greatest 

 is also the period when the eggs are most readily modified by 

 external agents. 



12. The relation of the susceptibility data to teratological de- 

 velopment is discussed at considerable length. It is shown that 

 those parts of the embryo having the highest susceptibility are 

 those which are most defective in teleost terata and that such 

 differential susceptibility is therefore the explanation of terato- 

 logical development. It is also shown that these same parts most 

 susceptible under extreme conditions may recover if conditions 

 permit and may develop while the less susceptible parts fail to 

 recover. Recovery forms of terata are thus just opposite in ap- 

 pearance to inhibited types. 



CITATIONS. 



Alvarez, W. C., and Starkweather, E. 



'18 The Metabolic Gradient underlying Intestinal Peristalsis. Amer. Jr. 



Physiol., Vol. 46, pp. 186-208. 

 Bellamy, A. W. 



'19 Differential Susceptibility as a Basis for Modification and Control of 



Early Development in the Frog. BIOL. BULL., Vol. 37, pp. 312-361. 

 Child, C. M. 



'153. Individuality in Organisms. University of Chicago Press. 

 'i5b Senescence and Rejuvenescence. University of Chicago Press. 

 '16 Experimental Control and Modification of Larval Development in the 

 Sea Urchin in Relation to the Axial Gradients. Jr. of Morph., Vol. 

 28, pp. 65-133. 



'17 Differential Susceptibility and Differential Inhibition in the Develop- 

 ment of Polychete Annelids. Jr. of Morph., Vol. 30, pp. 1-63. 

 Gee, Wilson. 



'16 Effects of Acute Alcoholization on the Germ Cells of Fundulus hetero- 

 clitus. BIOL. BULL., Vol. 31, pp. 379-406. 

 Hertwig, P. and G. 



'13 Beeinflussung der Mannlichen Keimzellen durch chemische Stoffe. Arch. 



f. mikro. Anat., Vol. 83, pp. 267-306. 

 Hyman, L. H. 



'16 An Analysis of the Process of Regeneration in Certain Microdrilous 

 Oligochaetes. Jr. Exp. Zool., Vol. 20, pp. 99-163. 



