THE PACTOES OP ORGANIC EVOLUTION. 31 



caterpillars, when placed on a mulberry-tree, often commit the strange mis 

 take of devouring the base of the leaf on which they are feeding, and 

 consequently fall down ; but they are capable, according to M. Eobinet, 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 &quot; (p. 304). 



Here are some instances of like meaning from volume ii. 



&quot; 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 

 good 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 

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

 when frightened, take flight like a young pheasant. . . . With domestic 

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

 the scapulae and f urcula, the length of the wings as measured from tip to tip 

 of the radius, are all reduced relatively to the same parts in the wild pigeon.&quot; 

 [After detailing kindred diminutions in fowls and ducks, Mr. Darwin adds] 

 &quot; The decreased weight and size of the bones, in the foregoing cases, is 

 probably the indirect result of the reaction of the weakened muscles on the 

 bones&quot; (pp. 297-8). &quot; Nathusius has shown that, with the improved races 

 of the pig, the shortened legs and snout, the form of the articular condyles of 

 the occiput, and the position of the jaws with the upper canine teeth pro 

 jecting in a most anomalous manner in front of the lower canines, may be 

 attributed to these parts not having been fully exercised. . . . These modi 

 fications of structure, which are all strictly inherited, characterise several 

 improved breeds, so that they cannot have been derived from any single 

 domestic or wild stock. With respect to cattle, Professor Tanner has 

 remarked that the lungs and liver in the improved breeds are found to be 

 considerably reduced in size when compared with those possessed by animals 

 having perfect liberty ; . . . The cause of the reduced lungs in highly-bred 

 animals which take little exercise is obvious&quot; (pp. 299-300). [And on pp. 

 301, 302 and 303, he gives facts showing the effects of use and disuse in 

 changing, among domestic animals, the characters of the ears, the lengths 

 of the intestines, and, in various ways, the natures of the instincts.] 



But Mr. Darwin s admission, or rather his assertion, 

 that the inheritance of functionally-produced modifications 

 has been a factor in organic evolution, is made clear not 

 by these passages alone and by kindred ones. It is made 

 clearer still by a passage in the preface to the second edition 

 of his Descent of Man. He there protests against that 

 current version of his views in which this factor makes no 

 appearance. The passage is as follows. 



