38 THE DOCTRINE OF DESCENT. 
system ; and any one who clings to the types as ideal 
and inalterable fundamental forms, falls into sad per- 
plexity how to dispose of his Radiata. 
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. 
