8 BIOLOGICAL SOCIETY OF WASHINGTON. 



into this category and are essentially sporadic. In the case of 

 circumcision, so often cited, they affect, at most, half the indi- 

 viduals of a race and only half of any one generation. 



There is not a particle of reason to believe that the excision 

 of a trifling scrap of cuticle from an infant would lead to any 

 physiological reaction worthy of attention. One might with 

 greater warrant seek such an effect in the growth of hair and 

 of the nails in civilized races accustomed to trim them. 

 Neither case has been shown to afford valuable evidence. 



There is no reason to deny that a pathologic incident of suf- 

 ficientlj' fundamental character may effect the progeny of an 

 individual, but it is of no consequence to the Dynamic hypo- 

 thesis whether it can be proven or not. 



Experience shows that it is not single mutilation or loss of 

 substance which results in permanent physiological reactions 

 so much as continued impacts which lead to locally increased 

 nutrition or local anaemia. 



The objection to reasoning drawn from pathologic cases is 

 not that it is not or may not be true, but that the cause affects 

 only individuals in trifling numbers. 



The forces invoked by Dynamic hj^pothesis, on the other 

 hand, affect every individual of a race and every generation 

 as long as the environment continues unchanged. Sporadic 

 modifications must always be finally swallowed up in the gen- 

 eral average of the organic type, unless carcfull}^ selected by 

 intelligent agencies. The steady pressure of telluric forces 

 lets no individual escape. 



On the coast of California the soft tertiary sandstones are 

 drilled by several species of boring mollusks, P/io/as, Lithophagus 

 and Petricola. In the course of time the borers die and leave their 

 closely fitting cells untenanted. Into these safe retreats the 

 young of several non-boring bivalves are in the habit of retiring. 



