78 THE FOUR PRINCIPLES OF SEGREGATION. 
fluctuating variations and culminating in a mutation that becomes 
stable. 
22. Selection and the Inheritance of Acquired Characters. 
The inheritance of functional variation, tf proved in any case, does not 
prove that selection has had no influence in shaping the characters of the 
same species. In a recent volume by J. T. Cunningham, entitled 
‘‘Sexual Dimorphism,”’ a large collection of very interesting facts on 
the subject of secondary sexual characters has been presented. It, 
however, seems to me that but little proof has been given of his con- 
tention that these characters have been produced, not by selection, 
but by the action of direct stimulation on the individual, facilitated 
and strengthened in successive generations by an increasing inher- 
itance of the effects of stimulus in previous generations. Whether 
acquired (t. e., functional) characters and tendencies can be inherited 
demands most careful investigation; but if it is found to be a fact it 
will not disprove the importance of the different forms of selection in 
determining the special kinds of response that the function awakens. 
Hertwig is undoubtedly right when he says that neither selection nor 
the inheritance of functional variations determines whether a given 
bee’s egg shall develop into a drone, a queen, or a worker, for the 
determining influence is the power of responding in different ways to 
different conditions. The question, however, remains as to why the 
workers of the Italian bee develop in such a way as to produce a long 
tongue, while certain other bees develop a comparatively short tongue. 
Hertwig admits that selection has had much to do with this diversity 
in the powers of response. 
In Prof. C. B. Davenport’s two volumes on ‘‘Experimental Mor- 
phology,” a large mass of facts illustrating the different responses of 
organisms to external conditions has been brought together, and in 
certain cases the effects are found to increase in successive generations 
when there is reason to believe that the increase is not due to selection. 
Though the inheritance of acquired characters may be proved by 
these experiments, I judge that Professor Davenport does not doubt 
that the different forms of selection have an important influence in 
shaping the specific characters of the same organisms. 
