THE FACTOES OF OEGANIC EVOLUTION. 11 



parts. The only pug-dog s skull is that of an individual 

 not perfectly adult; and though its traits are quite to the 

 point they cannot with safety be taken as evidence. The 

 skull of a toy-terrier has much restricted areas of insertion 

 for the temporal muscles ; has weak zygomatic arches ; and 

 has extremely small attachments for the masseter muscles. 

 Still more significant is the evidence furnished by the skull 

 of a King Charles s spaniel, which, if we allow three years 

 to a generation, and bear in mind that the variety must 

 have existed before Charles the Second s reign, we may 

 assume belongs to something approaching to the hundredth 

 generation of these household pets. The relative breadth 

 between the outer surfaces of the zygomatic arches is con 

 spicuously small ; the narrowness of the temporal fossae is 

 also striking; the zygomata are very slender; the temporal 

 muscles have left no marks whatever, either by limiting 

 lines or by the character of the surfaces covered ; and the 

 places of attachment for the masseter muscles are very 

 feebly developed. At the Museum of Natural History, 

 among skulls of dogs there is one which, though unnamed, 

 is shown by its small size and by its teeth, to have belonged 

 to one variety or other of lap-dogs, and which has the same 

 traits in an equal degree with the skull just described. 

 Here, then, we have two if not three kinds of dogs which, 

 similarly leading protected and pampered lives, show that 

 in the course of generations the parts concerned in clench 

 ing the jaws have dwindled. To what cause must this 

 decrease be ascribed ? Certainly not to artificial selection ; 

 for most of the modifications named make no appreciable 

 external signs : the width across the zygomata could alone 

 be perceived. Neither can natural selection have had any 

 thing to do with it; for even were there any struggle for 

 existence among such dogs, it cannot be contended that 

 any advantage in the struggle could be gained by an 

 individual in which a decrease took place. Economy of 

 nutrition, too, is excluded. Abundantly fed as such dogs 



