284 The New Factor in Organic Development . .May, 
in accordance with the modified direction of maximum strain 
or pressure. Hence the organism makes its own adapta- 
tions. Exceptional firmness is not designed to bear the 
strain, but the strain determines the firmness. 
Professor Bardeleben and Professor H. Meyer have also 
communicated to Dr. Roux, as the result of researches not 
yet fully completed, that the fibres of the sheaths inclosing 
the muscles run likewise in the direction of the greatest 
strain. None of these arrangements can conceivably be due 
to Natural Selection. Passing over other illustrations of 
adaptation to be explained neither teleologically nor by 
selection, we come to the heredity of the effects of functional 
adaptation. However great may be the combined efficacy 
of embryonic variation and of selection, there is at least one 
occurrence in the evolution of the animal kingdom which is 
distinctly beyond their power. There is one point of which 
we can maintain that a step in advance must have been 
taken, not successively in single organs, but simultaneously 
in almost all organs, since advantageous variation in one or 
other part would not have been sufficient. This point is the 
substitution of an aerial for an aquatic life. The more 
closely we examine the conditions perhaps thousands in 
number, involved in the transit from the water to the land, 
the more we are convinced that such a change, however 
gradual, cannot be effected by Natural Selection. An animal 
attempting this transit would be at first distressed by the 
unwonted weight of its body and limbs, no longer supported 
by the water. In attempts at locomotion it must use its 
muscles in different co-ordinations. The bones, the 
cartilages, and sinews have new and heavier duties. The 
blood, now exposed for the first time to the full force of 
gravitation tends to leave the brain and spinal marrow, and 
to counteract this tendency and prevent an anaemia of the 
nerve-centres the entire circulatory mechanism must undergo 
a change. Oxidation will be deficient, now the lungs alone 
have to supply the entire demands of the system. The 
drying of the skin, the gills, and the lateral organs will cause 
abnormal sensations. The perception of the external world 
will be modified, and the senses, for the time being, will be 
thrown almost into inactivity. It may be, of course, admitted 
that the first visits of the animal to the dry land would be 
brief, and that an abode in shallow pools, e.g. during the 
recess of the tide, might in some respeCts form a transition- 
stage. Still the necessity of a simultaneous change in 
almost every organ of the body is apparent. Now functional 
adaptation on any change of the vital conditions is capable 
