They haven't been deleted... We received a whole crapload of complaints from users who would rather not see that kind of content, so just like the straight and bisexual categories, we made the scat category an option you can turn on or off in your profile. Out of respect for the people who wish not to view such content, we set the default setting for this option to disabled. We apologise for any inconvenience this may cause.
If you wish to view this content, it is very quick and painless to enable those categories for your account. Simply click the "Profile" button at the top of the page, then check or uncheck the Straight, Bisexual, or Scat category accordingly, then scroll to the bottom of the page and click "Submit Changes". Once you do this, you should notice the "Scat" category pop up when you click the "Search" button, and that they'll also appear in the "Browse" function as well.EDIT:
It would appear that there was an update rolled out after the category filter option was added, which if I'm not mistaken, may make the scat categories not show in the picture browser with the "Browse" button, but I am not 100% sure of whether or not this was impacted by the update. I do know for sure though that if you change the settings under the "Profile" button at the top of the page, they WILL show up for you in the "Search" tab.