CHAP. XX Heredity 329 



has done momentous service in expounding. But for the 

 detailed theory by which he seeks to overcome the diffi- 

 culty which has been noticed above I refer those interested 

 to Weismann's Papers on Heredity (Trans. Oxford, 1889). 



4. The Inheritance of Acanired Characters. — {a) His- 

 torical. — We have seen that variations, or changes in char- 

 acter, may be constitutional, i.e. innate in the germ ; or 

 functional, i.e. due to use or disuse ; or environmental, i.e. 

 due to influences of nutrition and surroundings. Many 

 naturalists have believed that gains or losses due to any of 

 these three sources of change might be transmitted from 

 parent to offspring. But nowadays the majority, with 

 Profs. Weismann and Lankester at their head, deny the 

 transmissibility of either fiinctional or environmental 

 changes, and believe that inborn, germinal, or constitu- 

 tional variations alone are transmissible. 



This scepticism is not strictly modem. The editor, 

 whoever he was, of Aristotle's Historia Animalium, differed 

 from his master as to the inheritance of injuries and the 

 like. Kant maintained the non -inheritance of extrinsic 

 variations, and Blumenbach cautiously inclined to the same 

 negative position. In more recent times the veteran morpho- 

 logist His expressed a strong conviction against the inherit- 

 ance of acquired characters, and the not less renowned 

 physiologist Pfliiger is also among the sceptics. A few 

 sentences from Gallon (1875), whose far-sightedness has 

 been insufl&ciently acknowledged, may be quoted : " The 

 inheritance of characters acquired during the lifetime of the 

 parents includes much questionable evidence, usually diffi- 

 cult of verification. We might almost reserve our belief 

 that the structural cells can react on the sexual elements at 

 all, and we may be confident that at the most they do so in 

 a very faint degree — in other words, that acquired modifica- 

 tions are barely, if at all, inherited in the correct sense of 

 that word." 



But Weismann brought the discussion to a climax by 

 altogether denying the transmissibihty of acquired charac- 

 ters. 



(J)) Weismann's position. — Weismann's reasons for 



