304 ORDER AND SUCCESSION OF LIFE. 



they apply to the other, and, philosophically speaking, there 

 is no other mode of approaching the question. "We must 

 deal with life as we find it, and however much science may 

 fail in its demonstration, it is bound at least to make the 

 attempt. In the present state of human knowledge, rea- 

 son may be unable to grasp all the subtle and multifarious 

 conditions that regulate the development of vitality on our 

 globe ; under a deeper and broader insight into nature's 

 operations, the truth may begin to dawn upon us, and all 

 the sooner and clearer the sooner and more earnestly we 

 commence the investigation. 



Admitting the philosophy of the methods, we may still 

 be permitted to inquire how far any or all of these hypo- 

 theses are adequate to the solution of the problem ? In the 

 first place, it is obvious that external conditions operate 

 powerfully in the distribution of plants and animals, and 

 it is also admitted that they modify, in the long-run, the 

 species subjected to their operation; but it seems incredible 

 that they could transform one species into another species, 

 or one order into another order, without the aid of other 

 and more intimate physiological causes. Even combining 

 the force of external conditions with the use and disuse of 

 organs, and with the impulse of hereditary tendencies in 

 the embryonic or foetal stage of each successive generation, 

 the combination seems inadequate without some other factor 

 to keep the successive development in conformity with the 

 known plan of vitality. Should we add the operation of 

 natural selection, which is admittedly a powerful and ever- 

 active agent in the modification of species, still the questions 

 remain how plants and animals should exist in their 

 present ordinal arrangements, and how their appearance 

 in time should coincide, in the main, with these ordinal 

 arrangements 1 There are clearly some other factors over 

 and above all those which have yet been brought for- 



