DARWINISM DEFENDED. 147 



tion toward reduction of the organ would be of advantage 

 because of the saving in food which would be effected ! But 

 this is simply carrying the logic of the principle of advan- 

 tage to an illogical extreme, an extreme impossible to accept. 

 So Weismann devised the ingenious explanation of pan- 

 mixia or cessation of selection to account for degeneration. 

 That is, a rigid and persistent selective activity is as neces- 

 sary to maintain a specialisation as it was to produce it. 

 But even Weismann has found this explanation inadequate 

 and has, therefore, found a final and sufficient explanation 

 in his new theory of germinal selection. This last theory, a 

 refinement of Roux's theory of the battle of the parts, is 

 ingenious, suggestive, and thoroughly interesting, but un- 

 fortunately it is founded on certain assumptions concerning 

 the ultimate make-up of the germ-plasm and the behaviour 

 of the unit parts of it, the truth of which simply cannot be 

 tested. A strictly neo-Darwinian answer, that is, one based 

 solely on selection, is therefore hard to give. Plate, 10 after 

 an effective adverse criticism of the influence of the Weis- 

 mannian panmixia as an explanation of the structural reduc- 

 tion or atrophy of parts, concludes that such reduced or 

 rudimentary organs are to be explained "through the 

 inherited effects of disuse, the inherited effects of the influ- 

 ences of external factors, the inherited effects of the influence 

 of economy in nutrition, and, in a few cases, through re- 

 versed selection. The first three principles are only admissi- 

 ble under the assumption of the actuality of the inheritance 

 of individually acquired characters, and the fourth principle 

 has only a very subordinate importance." This is equivalent 

 to saying that the strict selectionist has no sufficient answer 

 to the objection under present consideration. One seems 

 forced to rely on Lamarckian factors for anything like a 

 satisfactory explanation of actual structural reduction of 

 useless organs. Tayler, 11 however, offers an explanation 

 for both ontogenic and phyletic degeneration, based on the 



