302 



LAWS OF VARIATION. 



Chap. XXIV. 



The epidermis on our hands is easily thickened, as every one 

 knows, by hard work. In a district of Ceylon the sheep have 

 " horny callosities that defend their knees, and which arise from 

 " their habit of kneeling down to crop the short herbage, and 

 " this distinguishes the Jaffna flocks from those of other portions 

 " of the island ; " but it is not stated whether this peculiarity 

 is inherited. 32 



The mucous membrane which lines the stomach is continuous 

 with the external skin of the body ; therefore it is not surprising 

 that its texture should be effected by the nature of the food 

 consumed, but other and more interesting changes likewise 

 follow. Hunter long ago observed that the muscular coat of the 

 stomach of a gull (Larus tridactylus) which had been fed for a 

 year chiefly on grain was thickened ; and, according to Dr. 

 Edmondston, a similar change periodically occurs in the Shetland 

 Islands in the stomach of the Larus argentatus, which in the 

 spring frequents the corn-fields and feeds on the seed. The 

 same careful observer has noticed a great change in the stomach 

 of a raven which had been long fed on vegetable food. In the 

 case of an owl (Strix grallarid) similarly treated, Menetries states 

 that the form of the stomach was changed, the inner coat became 

 leathery, and the liver increased in size. Whether these modi- 

 fications in the digestive organs would in the course of genera- 

 tions become inherited is not known. 33 



The increased or diminished length of the intestines, which 

 apparently results from changed diet, is a more remarkable 

 case, because it is characteristic of certain animals in their 

 domesticated condition, and therefore must be inherited. The 

 complex absorbent system, the blood-vessels, nerves, and muscles, 

 are necessarily all modified together with the intestines. Ac- 

 cording to Daubenton, the intestines of the domestic cat are 



one-third longer than those of the wild cat of Europe; and 



although this species is not the parent-stock of the domestic 

 animal, yet, as Isidore Geoffroy has remarked, the several species, 



32 'Ceylon/ by Sir J. E. Tennent, 



1859, vol. ii. p. 531. 



33 For the foregoing statements, see 

 Hunter's 'Essays and Observations,' 

 1861, vol. ii. p. 329; Dr. Edmondston, 



as quoted in Macgillivray's 'British 

 Birds,' vol. v. p. 550 : Menetries, as 

 quoted in Bronn's ' Geschicbte der 

 Natur,' B. ii. s. 110. 



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