There is also a call-up for 24-year-old Edinburgh flanker Ross Rennie who has just one cap to his name - won against Ireland in 2008.
Scotland, currently ranked seventh in the world, are set to face New Zealand, South Africa and Samoa next month.
Coach Andy Robinson said: "We have chosen this squad solely to prepare and play against New Zealand with everybody having an opportunity to be selected in the match 22.
"There is a very good balance to the squad.
"We set great store on improvement and Ruaridh has been working hard on his game.
"Joe has given some assured performances for Northampton when his team have been under pressure and he can play centre and wing which gives us options."
Scotland squad: Ansbro, Blair, Cairns, Evans, Grove, Jackson, Laidlaw, R Lamont, S Lamont, Lawson, Morrison, Parks, Paterson, Southwell, Thompson, Walker; Barclay, Brown, Cross, Dickinson, Ford, Gray, Hall, Hamilton, Hines, Jacobsen, Lawson, Low, MacDonald, MacLeod, Murray, Rennie, Strokosch, Vernon.