POTENCY IN RELATION TO DIFFERENTIATION 379 



limitation or inhibition. However, there is another aspect to determination, 

 namely, potency expression, which simply means potency release or develop- 

 ment. Potency expression, probably, is due to an activating stimulus (Spemann, 

 '38). Consequently, the individuation of a particular organ structure within 

 a larger system of organs is the result of two synchronous processes: 



( 1 ) inhibition of potency or potencies and 



(2) release or calling forth of a specific kind of potency (Wigglesworth, 

 '48). 



Associated with the phenomenon of potency inhibition or Hmitation is the 

 loss of power for regulation. Consequently, individuation and the loss of 

 regulative power appear to proceed synchronously in any group of cells. 



c. Prospective Potency and Prospective Fate 



Prospective fate is the end or destiny that a group of cells normally reaches 

 in its differentiation during its normal course of development in the embryo. 

 The presumptive epidermal area of the late blastula differentiates normally 

 into skin epidermis. This is its prospective fate. Its prospective potency, how- 

 ever, is greater, for under certain circumstances it may be induced, by trans- 

 plantation to other areas of the late blastula, to form other tissue, e.g., neural 

 plate cells or mesodermal tissues. 



d. Autonomous Potency 



Autonomous potency is the inherent ability which a group of cells possesses 

 to differentiate into a definite structure or structures, e.g., notochord, stomach, 

 or liver rudiments of the late blastula of the frog. 



Versatility of autonomous potency is the inherent ability which a group 

 of cells possesses to differentiate, when isolated under cultural conditions out- 

 side the embryo, into tissues not normally developed from the particular cell 

 group in normal development. In the amphibian late blastula this is true of 

 the notochordal and somitic areas of the chordamesodermal area, which may 

 give origin to skin or neural plate tissue under these artificially imposed 

 conditions. 



e. Competence 



Certain areas of the late amphibian blastula have the ability to differenti- 

 ate into diverse structures under the stimulus of varied influence. Conse- 

 quently, we say that these areas have competence for the production of this 

 or that structure. The word competence is used to denote all of the possible 

 reactions which a group of cells may produce under various sorts of stimula- 

 tions. The entodermal area of the late amphibian blastula and early gastrula 

 has great power for self-differentiation but no competence, whereas the gen- 

 eral, neural plate-epidermal area has competence but little power of self- 



