XL] SPECIFIC GENESIS. 271 



Dr. Bastian are confirmed by future investigation. Accord- 

 ing to his report, when the requisite conditions were sup- 

 plied, the transformations which appeared to take place 

 (from very low to higher organisms) were sudden, definite, 

 and complete. 



If this is so, there most probably exists in higher 

 forms a similar tendency to such change. That ten- 

 dency may indeed be long suppressed, and ultimately 

 modified by the action of heredity an action which would 

 increase in force with the increase in the perfection and 

 complexity of the organism affected. Still we might 

 expect that such changes as do take place would be also 

 sudden, definite, and complete. 



Moreover, as the same causes produce the same effects, 

 several individual parent forms must often have been 

 similarly and simultaneously affected. That they should 

 be so affected at least that several similarly modified 

 individuals should simultaneously arise has been seen to 

 be a generally necessary circumstance for the permanent 

 continuance of such new modifications. 



It is also conceivable that such new forms may be en- 

 dowed with excessive constitutional strength and viability, 

 and with generative prepotency, as was the case with the 

 black-shouldered peacock in Sir J. Trevelyan's flock. This 

 flock was entirely composed of the common kind, and yet 

 the new form rapidly developed itself " to the extinction of 

 the previously existing breed" 1 



Indeed, the notion accepted by both Mr. Darwin and 

 Mr. Herbert Spencer, and which is plainly the fact 

 (namely, that changes of conditions and incident forces, 

 within limits, augment the viability and fertility of indi- 



1 "Animals and Plants under Domestication," vol. i. p. 291. 



