From Webkinz Insider Wiki
Free trial memberships are available through the log in page for Webkinz World and more information about these trial memberships can be found at the Adoption Center.
Historical Information on the Webkinz Demo
In November, 2008, Ganz introduced the website www.webkinzdemo.com . This website was available to all for the first few days but was later changed so that people accessing the website from Canada or the United States would not be able to use this site.
Originally, the Webkinz Demo provided users with a free one-day trial of Webkinz World with limited features.
It first made its debut on the website www.webkinzdemo.com in November of 2008
After signing up for the Webkinz Demo, players received a free Webkinz pet -- a boy Mutt named Patches. The name and gender were both automatically chosen for the player and could not be changed. The Webkinz Mutt is currently unavailable outside of the Demo and can not be bought in stores. 
After adopting the Mutt, players received a Mutt-themed gift box containing a Red Dragster, a Burger and Bun, a Welcome balloon, and a Wish Token along with 5000 KinzCash and some furniture items. Both the Red Dragster and Burger and Bun could be previously obtained in the full Webkinz trial. Despite receiving a Wish Token, players soon discovered that the Wish Machine was a restricted feature in the Demo.
Shortly after the Demo was retired in the United States, some players were given the option to try out a limited account. As a starter pet, players were able to choose between a Domestic Cat or a Mutt. These pets could be named and given a gender just like normal Webkinz pets, but the trial was even more limited than the Demo. 
The Domestic Cat can not be bought in stores.
Those who used the Demo could only trade or befriend other Demo accounts. They could visit the Clubhouse but could not befriend a pet that wasn't a Domestic Cat or a Mutt.
Mutt Gets Member of the Day: http://www.webkinzinsider.com/forum/f146/members-confused-member-day-561307/
Domestic Cat Confirmed: http://www.webkinzinsider.com/forum/f146/webkinz-domestic-cat-confirmed-webkinz-insider-519800/