I have the latest generation ipad mini 2 but no siri and I can't find the microphone icon why please

Hi I am new to any Apple devices and would like to find out why I have not got SIRI on my ipad mini2. It is only two weeks old, has the latest IOS 8.4.1, is the latest generation but as far as I can see no Siri is installed. It is only WiFi and not a phone but everything I read says I should have it installed but I have not. I have tried all instructions I can find on the web etc but to no avail. Does this mean I have to have Cellular as well??? Please can someone help I would be most grateful!!😕. Thanks