462 PROCEEDINGS OF THE ACADEMY OF [1892. 



dogmatize. This absurd view amounts to the same thing as assert- 

 ing that organisms have the power to develop physiological pro- 

 cesses with conscious foresight, so as to avoid harm comiug to their 

 race ! This is on a par with Balfour's reasoning with respect to the 

 cause or reason of the existence of the polar bodies, namely, as a 

 preventive of parthenogenesis ! 



The criticisms of E. B. Poulton, in a foot-note on p. 425 of 

 Weismann's Essays, (Eng. Trans.) are similar to those offered long 

 ago by Dr. C. S. Tomes. .Poulton, like his predecessor, criticises 

 my views on the mechanical genesis of tooth-forms, without know- 

 ing what he is talking about, evidently not having read my paper. 

 He says: " It may be reasonably objected that the most elementary 

 facts concerning the development of teeth, prove that their shapes 

 cannot be altered during the life-time of the individual, except by 

 being worn away." " The shape is predetermined before the tooth 

 has cut the gum." " Hence the Neo-Lamarckian school assumes 

 not the transmission of acquired characters, but the transmission 

 of characters which the parent is unable to acquire!" Anything 

 more unfair or indiscriminating than the above could not be writ- 

 ten. I am charged with making statements I never made, and 

 never had the slightest intention of making. As I am the origina- 

 tor of the doctrine of the mechanical genesis of tooth-forms, I will 

 here say in reply that Poulton and Tomes cannot disprove that the 

 forms of the crowns of teeth of mammals are not altered in shape 

 in other vxn/s than by wear, or by means of stresses and consequent 

 permanent strains. If, as I have shown in my original essay, (Proc. 

 Acad. Nat. Sciences, 1878,) crystalline bodies can be permanently 

 bent and strained by persistent stresses, what proof is there to the 

 effect that even hard enamel caps cannot be so altered in the life- 

 time of the adult ? Moreover, I have shown that all the changes of 

 the crown-forms of the molars of the long series of Artiodacty Is, have 

 conformed with mechanical exactitude to the requirements of the 

 various degrees of latei'al motion of the jaws, and that where these 

 lateral motions were absent, lateral crown-modifications were also 

 absent. In other words, the degree of lateral modification is 

 correlated with the degree of lateral motion, or sweep of the jaws. 

 Later evidence has tended to show that the development of new 

 cusps and roots, in certain cases, takes place at points of maximum 

 wear in certain teeth in the domestic cat, as pointed out to me by 

 my colleague, Prof Jayne. 



