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
obj_id:integer
    rake:migrate

    ruby script/generate scaffold human name:string
passportNumber:string
    rake:migrate

    ruby script/generate scaffold dog name:string
registrationNumber:string
    rake:migrate

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

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

and run

    ruby script/server

and go to

    http://localhost:3000

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?