292 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. 31 



The mucous membrane which lines the stomach is con- 

 tinuous with the external skin of the body ; therefore it is 

 not surprising that its texture should be affected 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 gnll (Larus tridactylus) 

 which had been fed for a year chiefly on grain was thickened ; 

 and, according to Dr. Edmondston, a similar change periodi- 

 cally 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 

 grallaria), 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 modifications 

 in the digestive organs would in the course of generations 

 become inherited is not known. 32 



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. According 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, 



31 ' Ceylon,' by Sir J. E. Tennent, as quoted in Macgillivray's ' British 

 1859, vol. ii. p. 531. Birds,' vol. v. p. 550: Menetries, as 



32 For the foregoing statements, see quoted in Bronn's ' Geschiehte der 

 Hunter's 'Essays and Observations,' Natur,' B. ii. s. 110. 



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



