GENETICS 85 



acting on different materials can produce uniform 

 results, and since self -maintenance and propagation 

 are among the results of gene action, the genes 

 themselves may well undergo change in the normal 

 course of life. As this matter is presented here, it 

 seems highly speculative, but it is in no way out 

 of harmony with the known facts concerning mu- 

 tation. 



The field of embryology also provides us with 

 abundant material. Many eggs show a definite 

 distribution of cytoplasmic materials which is cor- 

 related with the distribution of organ-forming 

 substances during cleavage, others show a slight 

 differentiation involving at least a localization of 

 yolk, and even those in which the cytoplasm is 

 apparently homogeneous display evidence of its 

 differentiation in their polarity and symmetry. 

 The bearing of these matters on development is 

 considered by Conklin in the paper cited above, 

 where our limited understanding of them is indi- 

 cated in the following statement: "It would be 

 interesting to know to what extent this promor- 

 phology of the egg is the result of the activity of 

 genes within the egg-cell and how much is due to 

 the immediate environment, for, of course, both 

 intrinsic and extrinsic factors are involved in the 

 development of a spermatozoon or ovum as well as 

 in that of all later stages." ^^ But regardless of the 



" Am. Nat., Vol. LXIII, p. 15, 1929. 



