a few steps for a database with polymorphic association?

I thought it could be created in a few steps but it can't yet:

    rails poly
    cd poly

    ruby script/generate scaffold animal name:string obj_type:string

    ruby script/generate scaffold human name:string

    ruby script/generate scaffold dog name:string

and now change app/models/animal.rb to:

    class Animal < ActiveRecord::Base
      belongs_to :obj, :polymorphic => true

and run

    ruby script/server

and go to


I thought on the server then if I create an Michael, Human, J123456
and then Woofie, Dog, L23456

then the database will have entries in the Dogs table and "Humen" or
"Humans" table as well as in the Animals table? But only the Animals
table has records, Dogs and "Humen" do not for some reason. Is there
some steps missing?