1898] SPECTES, SEX, AND INDIVIDUAL 239 
the tracheal gills of aquatic larvae, for, although they are probably 
secondary adaptations in the larva, there are some who regard them 
as representing an ancestral series of organs from some of which the 
wings were derived. But if this be the case, the entire absence of 
wings and tracheal gills in the terrestrial larvae shows that the 
latter by no means recapitulate the ancestral history. Again, if the 
lees on the abdomen of the caterpillar behind the three pairs of 
thoracic legs are in any way related to the abdominal appendages of 
the ancestor, it is all the more certain that the maggots of the flies 
or of the ants, bees, and wasps, having no legs at all, cannot resemble 
the ancestor. In such cases the structure of the larva corresponds 
to its mode of life, and is much more different from any possible 
ancestor than is the adult. The individual does not here climb its 
own genealogical tree, unless it may be said to begin at the top and 
climb downwards. As for the origin of the modifications in the 
young stages, we have no evidence that their appearance was inde- 
pendent of the conditions ; the fact that the special structure only 
lasts as long as the special larval habits last, suggests strongly 
enough the direct dependence of the modifications on the conditions 
of life. 
To sum up the argument of which I have attempted to give an 
outline, its main points are these. Selection assumes the occurrence 
of variations: the variations must either be similarly indefinite and. 
promiscuous in all cases, or they must be different in different cases 
—that is, in different species, different sexes, different stages of life. 
If they are different in different cases, then selection is a very un- 
important matter, for the chief questions are evidently what are the 
differences and what made them different. To deny that the varia- 
tions have always been different in different cases is to deny the 
most evident facts: such denial might be possible when we consider 
only the difference between species, but is impossible when we study 
the differences between the sexes in the same species and between 
different stages in the same individual. In all cases the variations 
correspond to differences in habits and mode of life, and in many cases 
are of the same kind as the changes known to be produced in the 
individual by special stimulation or special activity of organs: this 
is true of many and probably of all cases of adaptation. The general 
conclusion is that adaptation is not produced indirectly by the selec- 
tion from indefinite variations, but directly by the influence of 
stimulation in modifying the growth of the parts or organs of the 
body. J. T. CUNNINGHAM. 
1 Morrap TERRACE, 
PENZANCE. 
