206 THE GENESIS OF SPECIES. [CHAP. 



in the fatty and earthy deposits in the coats of 

 arteries." 1 



He also considers it to be proved that, "Next to the 

 parts which are symmetrically placed, none are so nearly 

 identical in composition as those which are homologous. 

 For example, the backs of the hands and of the feet, or the 

 palms and soles, are often not only symmetrically, but 

 similarly, affected with psoriasis. So are the elbows, and 

 the knees ; and similar portions of the thighs and the arms 

 may be found affected with ichthyosis. Sometimes also 

 specimens of fatty and earthy deposits in the arteries 

 occur, in which exact similarity is shown in the plan, 

 though not in the degree, with which the disease affects 

 severally the humeral and femoral, the radial and peroneal, 

 the ulnar and posterior tibial arteries." 



Dr. William Budd 2 gives numerous instances of sym- 

 metry in disease, both lateral and serial. Thus, amongst 

 others, we have one case (William Godfrey) in which the 

 hands and feet were distorted. "The distortion of the 

 right hand is greater than that of the left, of the right foot 

 greater than that of the left foot." . In another (Elizabeth 

 Alford) lepra affected the extensor surfaces of the thoracic 

 and pelvic limbs. Again, in the case of skin disease illus- 

 trated in Plate III., " The analogy between the elbows and 

 knees is clearly expressed in the fact that these were the 

 only parts affected with the disease." 3 



Professor Burt Wilder, 4 in his paper on " Pathological 



1 "Lectures on Surgical Pathology," 1853, vol. i. p. 22. 



2 See " Medico-Chirurgical Transactions," vol. xxv. (or vii. of 2nd series), 

 1842, p. 100, PL III. 



3 Ibid., p. 122. 



4 See Boston Medical and Surgical Journal for April 5, 1866, vol. Ixxiv. 

 p. 189. 



