( xci ) 



transformation of species, may require raising into greater 

 prominence than they have hitherto occupied. The fact that 

 the struggle for life is not only between living forms but also 

 between the organism and its physical environment was 

 clearly enough perceived by the founders of the theory of 

 natural selection, although they attributed greater weight to 

 the former ; the tendency of my remarks is simply to give 

 renewed emphasis to the action of the physical as distinguished 

 from the organic environment. In contemplating the fact 

 that only a small number of the whole offspring reach maturity, 

 we must bear in mind the possibility of physiological unfitness 

 being a cause of elimination* 



I am most anxious to avoid the appen-rance of founding a 

 new sect, and I again remind you, in concluding, that I am 

 not laying down any new law ; neither do I assert that 

 physiological correlation is a proved factor. It is my 

 object simply to suggest that such a factor may pro- 

 fitably form the subject of experimental investigation. 

 Until we are enabled to penetrate further into the latent 

 mysteries of the living organism and the relationship between 

 its inner activities and the external conditions of its existence, 

 it appears to me that discussions as to which out of a group 

 of correlated characters, some obvious and others latent, is to 

 be regarded as the cause of its survival are likely to prove 

 barren. If, on the other hand, my remarks do but prompt 

 further inquiry into the subject of physiological variability — 

 if they only bring about a closer nipjirochement between 



* Tbe problem as it presents itself for investigation may be put in other- 

 words tbus : — Supposing all the offspring of one pair to be kept, under 

 identical physical conditions, supplied with plenty of food, and removed 

 from all competition with other forms of lif>', would all the individuals 

 reach maturity and, if not, what influence would determine which should, 

 survive and which succumb ? It seems but reasonable to suppose that 

 physiologii^al unfitness for those particular physical conditions would be one 

 important factor in determining survival. In any experiments undertaken 

 in this direction the possible selecting action of micro-organisms njust be 

 taken into consideration. It is generally believed, for instance, as the rnsult 

 of Pasteur's investigations, that the larvae of Bouibyx mori whi.h spin 

 white s-ilk are less liable to the attack of fuugoi 1 disease than those which 

 spin yellow cocoons. If this be the case the coh'ur ot the silk is a correlate 

 of some constitutional or physiological character of (he larra. 



