Chap XXIV. EFFECTS OF USE AND DISUSE. 289 



been kept during many centuries closely confined, emerge from their 

 cocoons with their wings distorted, incapable of flight, often greatly 

 reduced in size, or even, according to Quatrefages, quite rudimentary. 

 This condition of the wings may be largely owing to the same kind 

 of monstrosity which often affects wild Lepidoptera when artificially 

 reared from the cocoon ; or it may be in part due to an inherent 

 tendency, which is common to the females of many Bombycidse, to 

 have their wings in a more or less rudimentary state ; but part of 

 the effect may be attributed to long-continued disuse. 



From the foregoing facts there can be no doubt that with 

 our anciently domesticated animals, certain bones have in- 

 creased or decreased in size and weight owing to increased or 

 decreased use ; but they have not been modified, as shown in 

 the earlier chapters, in shape or structure. With animals 

 living a free life and occasionally exposed to severe compe- 

 tition the reduction would tend to be greater, as it would be 

 an advantage to them to have the development of every 

 superfluous part saved. With highly-fed domesticated animals, 

 on the other hand, there seems to be no economy of growth, 

 nor any tendency to the elimination of superfluous details. 

 But to this subject I shall recur. 



Turning now to more general observations, 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 projecting in a most anomalous manner in front of the 

 lower canines, may be attributed to these parts not having 

 been fully exercised. For the highly-cultivated races do not 

 travel in search of food, nor root up the ground with their 

 ringed muzzles. 22 These modifications of structure, which 

 are all strictly inherited, characterise several improved 

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

 domestic stock. AVith 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 ;" 23 



22 Xathusius, ' Die Racen des Nathusius : ' Der Schadel des Ma&ken« 



Schweines,' 1860, s. 53, 57 ; ' Vor- schweiues,' 1870. 

 studien .... Schweineschadel,' 1864, 23 'Journal of Agriculture of High 



s. 103, 130, 133. Prof. Lucae supports land Soc.,' July, 1860, p. 321. 

 and extends the conclusions of Von 



