196 Ani7nal Life and Intelligence. 



fed on sops, have no need to use to any large extent the 

 jaw-muscles. In this case, he argues, the principle of 

 economy is not likely to be operative, since the pampered 

 pet habitually overeats, and has therefore abundant nutri- 

 ment and to spare to keep up the jaws. It is possible, 

 however, that artificial selection has here been a factor. 

 There may have been a competition among the old ladies 

 who keep such pets to secure the dear little dog that never 

 bites, while the nasty little wretch that does occasionally 

 use his jaws for illegitimate purposes may have been 

 speedily eliminated. Pet dogs are, moreover, a pampered, 

 degenerate, and for the most part unhealthy race, often 

 deteriorated by continued in-breeding, so that we must not 

 build too much on Mr. Spencer's observations, interesting 

 as they undoubtedly are. 



There is one feature about the reduction of organs 

 which must not be lost sight of. They are very apt to 

 persist for a long time as remnants or vestiges. The 

 pineal gland is the vestigial remnant of a structure con- 

 nected with the primitive, median, or pineal eye. The 

 whalebone whales and the duck-bill platypus have teeth 

 which never cut the gum and are of no functional value. 

 With regard to these, it may be asked — If disuse leads to 

 the reduction of unused structures, how comes it that 

 it has not altogether swept away these quite valueless 

 structures ? In considering this point, we must notice the 

 unfortunate and misleading way in which disuse is spoken 

 of as if it were a positive determinant, instead of the mere 

 absence of free and full and healthy exercise. Few will 

 question the fact that in the individual, if an organ is to 

 be kept up to its full standard of perfection, it must be 

 healthily and moderately exercised; and that, if not so 

 exercised, it will not only cease to increase in size, but will 

 tend to degenerate. The healthy, functionally valuable 

 tissue passes into the condition of degenerate, comparatively 

 useless tissue. Now, those who hold that the inheritance 

 of functioiial modifications is still a tenable hypothesis, 

 carry on into the history of the race that which they find 



