i8 ARE THE EFFECTS OF USE INHERITED? 



immediate object of proving that there is " no 

 concomitant variation in co-operative parts," even 

 when " formed out of the same tissue, like the 

 crab's eye and its peduncle" (pp. 12-14, 23, 33). 

 It escapes his notice, however, that in two out 

 of his three cases it is disuse, or diminished 

 use, which fails to cause concomitant variation or 

 proportionate variation. 



THE GIRAFFE, AND NECESSITY FOR 

 CONCOMITANT VARIATION. 



Having unwittingly shown that lessened use of 

 closely-connected and co-operative parts does not 

 cause concomitant variation in these parts, Mr. 

 Spencer concludes that the concomitant varia- 

 tion requisite for evolution can only be caused 

 by altered degrees of use or disuse. He elabor- 

 ately argues that the many co-ordinated modifi- 

 cations of parts necessitated by each important 



