REPRESENTATIVE LAMARCKIANS 257 



third and similar example is furnished by the elbow- 

 joint of the Quadrumana and Diplarthra." 



Cope also mentions the evolution of the foot in dig- 

 itigrades and plantigrades and the variations in the 

 number of toes: "The types with reduced digits are 

 dwellers on dry land, and those that have more nu- 

 merous digits are inhabitants of swamps and mud, or 

 are more or less aquatic." . . , 6 



He also points out the correspondence between the 

 various dental types and the mode of mastication, etc. 

 Finally we come to Cope's hypothesis as to the forma- 

 tion of the vertebral column: "If we now imagine 

 that either the integuments, or an axial rod of a 

 worm-like animal has become the seat of a calcareous 

 or chitinous deposit, it is evident that the movements 

 of the animal in swimming or creeping must have in- 

 terrupted the deposit at definite points of its length. 

 At the lines of interruption, joints would be formed, 

 and if the movements were habitually symmetrical, 

 these interruptions would be equidistant. Thus the 

 segmentation of the osseous sheath of the chorda dor- 

 salis in both primitive fishes and batrachians has been 

 accomplished in wedge-shaped tracts precisely as may 

 be observed in the folding of a tolerably stiff sleeve 

 of a coat which ensheathes the arm, under the influ- 

 ence of lateral flexures. The wedge-shaped tracts are 

 superior and inferior, the apices directed towards each 



• The Primary Factors of Evolution, pp. 289-309. 



