A COMMENTARY ON LAMARCKISM 



completely protected position on the ordinary skin of the chest. 



So much for the evidence that the difference between sole 

 and body epithelium is of developmental origin, i.e. is an in- 

 herited difference between the somatic cells that arise by 

 fission of the zygote. It must now be shown that even if the 

 difference were not of developmental origin, it would be almost 

 exactly reproduced within an individuaPs own lifetime as a 

 response to differences in the habit of use; it must be sho^vn 

 that if guinea-pigs or human beings were in fact born with a 

 thin and delicate epithelium on the soles of their feet, ordinary 

 use would soon toughen and thicken it. 



There can be no reasonable doubt that this would be so, 

 because a normally quiescent epidermal epithelium can easily 

 be induced to thicken in response to chronic irritation. Corns 

 are so formed on the thin skin of the dorsum of the toes; 

 callosities on the hands develop as a response to chronic chafing. 

 A com has a histological structure very closely similar 

 to that of the skin on the heel of the foot, with a deep, strati 

 fied, vigorously dividing epidermis, a thick pad of compact 

 cuticle, and tall, steeply rising dermal papillae. The difference 

 is that corns and callosities do not last much longer than the 

 mechanical stimuli that provoked their formation; corns sub- 

 side with the wearing of shoes that fit; callosities may be cured, 

 as they may also be avoided, by wearing gloves. Evidently the 

 epidermis has the capacity to thicken in response to mech- 

 anical abuse. In the epidermis of the sole or heel, this thicken- 

 ing is developmentally anticipated and does not depend for its 

 maintenance upon the continued stress of use; and yet, were 

 it not so anticipated, stress of use could be relied upon to 

 reproduce it faithfully. All adaptations that are open to a 

 Lamarckian interpretation have this distinctive character: 

 that they represent differences of developmental origin that 

 can be faithfully mimicked within an individuaPs own lifetime 

 by differences in mode of use. 



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