38 THE DOCTRINE OF DESCENT. 



instance, tracheae with those of the Annelida as the lateral 

 organs. 



The combination is inexplicable ' and paradoxical from 

 the point of view of the old system. 



Example after example might be thus accumulated 

 to show that the rigid partitions of the system are 

 scarcely raised before they are again broken down in 

 every direction ; and this in direct ratio with the increase 

 of special science. As before said, descriptive natural 

 history necessarily gained this experience. It then 

 spoke of exceptions and deviations, without being able 

 to adduce any reason why the classes and types should 

 be able to break through their limits, and indeed most 

 frequently without feeling any need of accounting for 

 the failure of the rigid system. 



