1898] SPECIES, 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 

 leg*; 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 Morrab Terrace, 

 Penzance. 



