198 THE GENESIS OF SPECIES. [CHAP. 



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

 be found affected with icthyosis. 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 de- 

 gree, with which the disease affects severally the humeral 

 and femoral, the radial and peroneal, the ulnar and pos- 

 terior tibial arteries." 



Dr. William Budd 32 gives numerous instances of sym- 

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

 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 



Prof. Burt Wilder, 34 in his paper on " Pathological Po- 

 larities," strongly supports the philosophical importance 

 of these peculiar relations, adding arguments in favor of 

 antero-posterior homologies, which it is here unnecessary 

 to discuss, enough having been said, it is believed, to thor- 

 oughly demonstrate the existence of these deep internal 

 relations which are named lateral and serial homologies. 



What explanation can be offered of these phenomena ? 

 To say that they exhibit a " nutritional relation " brought 

 about by a " balancing of forces " is merely to give a new 

 denomination to the unexplained fact. The changes are, 

 of course, brought about by a " nutritional " process, and 



32 See " Medico-Chirurgical Transactions," vol. xxv. (or vii. of 2d 

 series), 1842, p. 100, PL III. 



33 Med.-Chinirg. Trans, vol. xxv. (or vii. of 2d series), 1842, p. 122. 



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

 Ixxiv., p. 189. 



