210 The American Naturalist. [March, 
tion of the limb; other elements remain zz statu quo, orin a 
state of balance where their adjustments are perfect. 
There is also a large class of adaptive, characters, both in 
animals and plants, upon which the law of individual adaptive vari- 
ation operates very obscurely if at all,—e. g., protective coloration 
How Far Does Race Variation Follow Individual Variation ? 
—The study of individual variations led Spencer to the conclusion 
that all higher forms (of vertebrates) have arisen by the super- 
posing of adaptations upon adaptations.” The students of verte- 
brate paleontology observe that race adaptations conform so 
closely to the laws of progressive individual variation that they 
are impelled to seek the explanation of the origin of various 
structures in the reactions occurring in individuals. Here are the 
definite lines of variations spoken of above. 
But if they jump to the conclusion that individual variations 
are the cause of these race variations, may they not fall into the 
old fallacy of post hoc ergo propter hoc? For every genetic line 
will be found to exhibit variations in definite lines of adaptation 
and many of these lines of variation occur in characters in which 
no individual adaptation can be observed.” Now there is no 
theoretical difficulty in supposing that the three classes of variations 
have different modes of origin, byt in order to demonstrate the 
‘probability of a causal relation between individual and race varia- 
tions of Class III. it is further necessary to show: 1. That in this © 
special class of characters, in which obvious mechanical or 
dynamical principles are operative, race variations invariably con- 
form to individual variations; for if some of these characters 
do not conform, other principles must be in operation. That is, 
-if we once invoke the Lamarckian principle, we must apply it 
consistently to every case. 2. That no definite lines of variation 
arise in characters of this class without the antecedent operation 
of these individual reactions. These first tests of invariable ante- 
.cedence.and consequence would lend a high degree of probability 
3° A beautiful example of the effects of use in producing joints in the tail fins of fishes 
“has been given by Ryder. Proc. Am. Phil. Soc., Nov. 21, 1889. 
oe As quoted by Ryder from ‘British and Foreign Medico-Chirurgical Review, Oct., 
53 Such as are seen in the adaptations of ‘mimicry and protective coloration, 
