Chap. XXIV. ARRESTED DEVELOPMENT AND RUDIMENTS. 315 



having been long and steadily selected, though such selection 

 is admitted to be indispensable for the improvement of any- 

 other character, it is not surprising that man has done little 

 in the acclimatisation of domesticated animals and cultivated 

 plants. We need not, however, doubt that under nature new 

 races and new species would become adapted to widely different 

 climates, by spontaneous variation, aided by habit, and regulated 

 by natural selection. 



Arrests of Development : Rudimentary and Aborted Organs. 



These subjects are here introduced because there is reason to believe 

 that rudimentary organs are in many cases the result of disuse. Modifica- 

 tions of structure from arrested development, so great or so serious as to 

 deserve to be called monstrosities, are of common occurrence, but, as they 

 differ much from any normal structure, they require here only a passing 

 notice. When a part or organ is arrested during its embryonic growth, 

 a rudiment is generally left. Thus the whole head may be represented by 

 a soft nipple-like projection, and the limbs by mere papillae. These rudi- 

 ments of limbs are sometimes inherited, as has been observed in a dog. 81 



Many lesser anomalies in our domesticated animals appear to be due to 

 arrested development. What the cause of the arrest may be, we seldom 

 know, except in the case of direct injury to the embryo within the egg or 

 womb. That the cause does not generally act at a very early embryonic 

 period we may infer from the affected organ seldom being wholly aborted, 

 — a rudiment being generally preserved. The external ears are represented 

 by mere vestiges in a Chinese breed of sheep ; and in another breed, the 

 tail is reduced " to a little button, suffocated, in a manner, by fat." 82 In 

 tailless dogs and cats a stump is left; but I do not know whether it 

 includes at an early embryonic age rudiments of all the caudal vertebrae. 

 In certain breeds of fowls the comb and wattles are reduced to rudi- 

 ments ; in the Cochin-China breed scarcely more than rudiments of spurs 

 exist. With polled Suffolk cattle, " rudiments of horns can often be felt 

 " at an early age ; " 83 and with species in a state of nature, the relatively 

 greater development of rudimentary organs at an early period of life is 

 highly characteristic of such organs. With hornless breeds of cattle 

 and sheep, another and singular kind of rudiment has been observed, 

 namely, minute dangling horns attached to the skin alone, and which are 

 often shed and grow again. With hornless goats, according to Desmarest, 84 



81 Isid. Geoffroy St. Hilaire, ' Hist. ™ Youatt on Cattle, 1834, p. 174. 

 Nat. des Anomalies,' 1836, torn. ii. pp. ^ 'Encyclop. Method., ' 1820, p. 483 : 

 210, 223, 224, 395 ; ' Philosoph. Trans- see p. 500, on the Indian zebu casting 

 act.,' 1775, p. 313. it s horns. Similar cases in European 



82 Pallas, quoted by Youatt on Sheep, cattle were given in the third chapter. 

 p. 25. 



