86 



THE AMERICAN NATURALIST [Vol. LI 



dueed several offspring. Where a parent of the low group had been 

 found to bring forth high progeny, that parent was removed. Simi- 

 larly, if a parent with a high number of spines is found to produce 

 offspring with low numbers, this parent was removed. Thus in the 

 low group we gradually tend to accumulate a set of individuals (1) 

 which in the past have produced progeny with low numbers of spines; 

 (2) whose ancestors for several generations back are individuals with 

 low numbers of spines. In the liigh group the reverse conditions are 

 fulfilled. 



From the time this change in method was made until the 

 end of the experiment, selection produced a marked 

 effect, differentiating clearly high spine groups and low 

 spine groups. 



The significance of this result seems to me to lie in the 

 fact that with the new method of selection described by 

 Jennings the ultimate basis of selection was changed 

 from the soma to the germ. Because after the change in 

 method what primarily determined the selection of any 

 particular individual for further reproduction was not 

 its own spine number, but instead its demonstrated ability 

 to produce offspring with a particular spine number (or 

 nearly that number). A low spine parent was allowed 

 to survive and reproduce not alone or primarily because 

 it had few spines but only when in addition it was surely 

 known to produce low spine progeny. This is indeed a 

 different basis than that which merely selects individuals 

 because of their somatic spine number and nothing else. 

 It abruptly and completely transfers the selection from 

 soma to germ. As has already been pointed out earlier 

 in this paper (p. 5), there can be no question about the 

 efficacy of selection which operates on a directly gametic 

 rather than a somatic basis. This idea of making the 

 basis of selection the a])ility to trnnsTnit to tlio progeny 

 the desired quality is one wliifh the writer lias for a good 

 many years stronirly ndvopatod as the only ronlly useful 

 or hoix'fiil nicflMMl In tli.' pra-'tipnl 1)rcorilno. of higher 

 animals. Tri liis own with ponltiy'"' it has been 



crowned witli tlie liigliost })raptical snccoss. Beyond 



53 Pearl, E., Amer. Nat., Vol. XLTX, pp. 306-317, 1915. 



