THE OPINIONS OF NEO-LAMARCKIANS. 523 



sis in the premolars and pocketing of the incisor- 

 enamel ; (<) all new elements and forms at first so 

 minute as to be barely visible, immediately selected 

 and accumulated ; (Y) in the same individuals favor- 

 able variations in the proportions of the digits involv- 

 ing readjustments in the entire limbs and skeleton, all 

 coincident with those in the teeth ; (//) finally, all the 

 above new variations, correlations, and readjustments 

 not found in the hereditary germ-plasm of one period, 

 but arising fortuitously by the union of different strains, 

 observed to occur simultaneously and to be selected at 

 the same rate in the species of the Rocky Mountains, 

 the Thames Valley, and Switzerland ! These assump- 

 tions, if anything, are understated." 



I have already referred to the contribution by Dall 

 to the doctrine of kinetogenesis which has resulted 

 from his investigations of the origin of the characters 

 of the lamellibranchiate (or pelecypod) Mollusca. 1 He 

 observes : "In reflecting upon the origin of the com- 

 plicated mechanical arrangements in bivalves which 

 we call the hinge, I have come to the conclusion that 

 here, as in the cases of the mammalian foot and tooth 

 elaborated so clearly by Cope and Ryder, we have the 

 result of influences of a mechanical nature operating 

 upon an organ or apparatus in the process of develop- 

 ment. . . . The shell is in one sense the product of se- 

 cretion from the mantle, as the mammalian tooth is 

 derived from the ectoderm of the jaw, or the skeleton 

 from the periosteum and cartilages. Both are that 

 and much more. It would be as reasonable to say 

 that a steam boiler in process of construction is the 

 product of the boy inside who holds the rivet-heads, 

 as to claim that the shell has no more significance 



3 American Journal of Science and Arts, December, 1889, p. 447. 



