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THE AMEBIC AN NATUBALIST [Vol. XLIX 



feet and tail of P. m. rubidus, for example, might be at- 

 tributed to its (assumed) greater activity. Unfortu- 

 nately for this theory, the pelvis and femur of rubidus is 

 no greater (slightly smaller, it would seem) than in the 

 other races. Had the enlargement of the foot been 

 due to greater functional activity the skeletal parts named 

 would probably have also undergone an increase in size. 



From a series of measurements upon the skeletons of 

 wild and domestic fowls and rabbits, Darwin inferred a 

 relative decrease in the size of the wings of the former 

 and of the cranial capacity of the latter, under the in- 

 fluence of domestication. These conclusions may well be 

 true, but the evidence offered seems to be open to several 

 objections. (1) They are based on too small numbers 

 and lack the precision demanded by modern statistical 

 work. (2) We can only infer the exact nature of the wild 

 stock from which the domesticated races are descended. 

 (3) We can not judge of the extent to which artificial se- 

 lection may have played a part in bringing about these 

 differences. It was perhaps considerable. (4) We do not 

 know how much of this modification results from use or 

 disuse during the animal's own lifetime. It might be 

 contended that the change was not congenital at all. 



Lapicque and Girard have, in the main, demonstrated 

 a smaller cranial capacity in domesticated animals as 

 compared with wild ones, but aside from the more rig- 

 orous statistical methods employed by these authors, the 

 biological significance of their results is open to the same 

 objections as I have stated in the case of Darwin's. 



Hatai 21 has shown that the albino rat has a smaller 

 brain than the wild Norway rat, when individuals of the 

 same size are compared. This proves nothing definite, 

 however, as to the effects of domestication, a fact which 

 the author recognizes. The deficient brain of the albino 

 may have been part of the same mutation which brought 

 about the albinic condition. Or it may have resulted 

 in part from the selection of tamer individuals. Or the 



2i Anatomical Eecord, Vol. 3, 1909, p. 245. 



