774 THE POPULAR SCIENCE MONTHLY. 



appear in many cases to have been potent in their effects" (p. 131). "When 

 discussing special cases, Mr. Mivart passes over the effects of the increased use 

 and disuse of parts, whicli I have always maintained to be highly important, and 

 have treated in my ' Variation under Domestication' at greater length than, as 

 I believe, any other writer" (p. 176). " Disuse, on the other hand, will account 

 for the less developed condition of the whole inferior half of the body, including 

 the lateral fins" (p. 188). "I may give another instance of a structure which 

 apparently owes its origin exclusively to use or habit" (p. 188). "It appears 

 probable that disuse has been the main agent in rendering organs rudimentary " 

 (pp. 400—401). " On the whole, we may conclude that habit, or use and disuse, 

 have, in some cases, played a considerable part in the modification of the consti- 

 tution and structure ; but that the effects have often been largely combined with, 

 and sometimes overmastered by, the natural selection of innate variations " 

 (p. 114). 



In his subsequent work, The Variation of Animals and Plants 

 under Domestication, where he goes into full detail, Mr. Darwin gives 

 more numerous illustrations of the inherited effects of use and disuse. 

 The following are some of the cases, quoted from volume i of the first 

 edition : 



Treating of domesticated rabbits, he says : — " the want of exercise has ai>par- 

 ently modified the proportional length of the limbs in comparison with the 

 body" (p. 116). "We thus see that the most important and complicated organ 

 [the brain] in the whole organization is subject to the law of decrease in size 

 from disuse" (p. 129). He remarks that in birds of the oceanic islands " not 

 persecuted by any enemies, the reduction of their wings has probably been 

 caused by gradual disuse." After comparing one of these, the Wiiter-hen of 

 Tristan d'Acunha, with the European water-hen, and showing that all the bones 

 concerned in flight are smaller, he adds — "Hence in the skeleton of this natural 

 species nearly the same changes have occurred, only carried a little further, as 

 with our domestic ducks, and in this latter case I presume no one will dispute 

 that they have resulted from the lessened use of the wings and the increased use 

 of the legs " (pp. 286-7). "As with other long-domesticated animals, the in- 

 stincts of the silk-moth have suffered. The caterpillars, when placed on a mul- 

 berry-tree, often commit the strange mistake of devouring the base of the leaf 

 on which they are feeding, and consequently fall down ; but they are capable, 

 according to M. Robinet, of again crawling up the trunk. Even this capacity 

 sometimes fails, for M. Martins placed some caterpillars on a tree, and those 

 which fell were not able to remount and perished of hunger; they were even 

 incapable of passing from leaf to leaf " (p. 304). 



Here are some instances of like meaning from volume ii. 



" In many cases there is reason to believe that the lessened use of various 

 organs has affected the corresponding parts in the offspring. But there is no 

 pood evidence that this ever follows in the course of a single generation. . . . 

 Our domestic fowls, ducks, and geese have almost lost, not only in the indi- 

 vidual but in the race, their power of flight; for we do not see a chicken, when 

 frightened, take flight like a young pheasant. . . . Witli domestic pigeons, the 

 length of the sternum, the prominence of its crest, the length of the scapulaj 

 and furcula, the length of the wings as measured from tip to tip of the radius, 



