A FEATHER. 693 



but a power-engine placed on wheels — not the improved power-engine 

 of the present day, but an unimproved and rudimentary form. We 

 might trace the history of other forms in the same way, until we had 

 found the one source for them all. 



In this case there can be no genetic connection ; each engine is 

 an independent thing, and the only connection is an ideal one in the 

 minds of the inventors ; that is, the idea of the steam-engine has gone 

 through a process of evolution, expansion, and perfection, and most 

 of the steps in the process have been embodied in real engines, so 

 that together they form a manifestation or record of the changes that 

 the idea has undergone. 



According to the theory of which Agassiz is the most celebrated 

 advocate, the phenomena of life are to be explained in a somewhat 

 similar way. Recognizing all the facts which seem to indicate the 

 evolution of the animal kingdom, and being himself the discoverer of 

 very many of them, he says that the evolution is simply the evolution 

 of an idea in the mind of the Creator, which idea has been embodied 

 in material form in such a way that it can be traced by the study of 

 the animals that form its expression. 



The other theory may also be illustrated by an example : When 

 we compare languages which philologists tell us have descended from 

 one parent tongue, we are attracted by their differences only, and it 

 needs careful study and comparison to understand the similarity of 

 plan which underlies them all ; but when their history is traced it is 

 seen that they were originally the same, and have become different as 

 the races using them have become more widely separated, and, com- 

 ing under new and widely different physical conditions, have diverged 

 in their habits, feelings, thoughts, and associations, and have required 

 different forms of speech to supply their need. Here, unlike the case 

 of the steam-engines, the language has been the same all the time, and, 

 although men have been the means by which the change has been 

 effected, they have not been the intelligent cause, but have been un- 

 consciously acted upon by agencies around them. 



According to the theory with which Darwin is identified, although 

 he is not by any means the author, but has simply removed some 

 of the most serious objections, all the different forms of life have 

 been evolved from one source in substantially the same way that lan- 

 guages have originated ; as animals become exposed to new conditions, 

 new varieties adapted to these conditions arise, and, as animals thus 

 grow different, the parent unimproved forms are unable to struggle 

 with their more perfect descendants and become extinct, so that the 

 animals which would connect dissimilar forms are no longer in exist- 

 ence. 



The evidence necessary for the perfect establishment of either of 

 these theories does not seem to have been obtained as yet, and we can 

 only decide provisionally, according to probabilities ; but the discus- 



