"Today's selection is a good indication of the depth and level of competition we currently have in Scotland," Townsend said in a statement.
The group included 14 players who featured in the 31-man squad that reached the quarter-final of the 2015 tournament in England, with Townsend likely to add two more players.
"We made a conscious decision to keep squad numbers low, which enables us to do more work with those most likely to be on the plane to Japan," Townsend added.
"We're really excited to work with this group of players who will now compete hard for a place in the final 31-man group going to the World Cup."
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Scotland play two tests each against France and Georgia starting in August, before taking on Ireland in their World Cup Pool A opener in Yokohama on Sept. 22.
Scotland's 42-man World Cup training squad:
FORWARDS (23)
John Barclay (Edinburgh) – 71 caps
Simon Berghan (Edinburgh) – 19 caps
Jamie Bhatti (Glasgow Warriors) – 13 caps
Magnus Bradbury (Edinburgh) – 7 caps
Fraser Brown (Glasgow Warriors) – 42 caps
Allan Dell (Edinburgh) – 22 caps
Matt Fagerson (Glasgow Warriors) – 3 caps
Zander Fagerson (Glasgow Warriors) – 19 caps
Grant Gilchrist (Edinburgh) – 33 caps
Gary Graham (Newcastle Falcons) – 2 caps
Jonny Gray (Glasgow Warriors) – 51 caps
Stuart McInally (Edinburgh) – 27 caps
Willem Nel (Edinburgh) – 29 caps
Gordon Reid (London Irish) – 34 caps
Jamie Ritchie (Edinburgh) – 10 caps
Sam Skinner (Exeter Chiefs) – 5 caps
Grant Stewart (Glasgow Warriors) – uncapped
Blade Thomson (Scarlets) – uncapped
Josh Strauss (Sale Sharks) – 22 caps
Ben Toolis (Edinburgh) – 18 caps
George Turner (Glasgow Warriors) – 5 caps
Hamish Watson (Edinburgh) – 25 caps
Ryan Wilson (Glasgow Warriors) – 43 caps
BACKS (19)
Darcy Graham (Edinburgh) – 4 caps
Nick Grigg (Glasgow Warriors) – 9 caps
Chris Harris (Newcastle Falcons) – 8 caps
Adam Hastings (Glasgow Warriors) – 11 caps
Stuart Hogg (Glasgow Warriors) – 67 caps
George Horne (Glasgow Warriors) – 4 caps
Pete Horne (Glasgow Warriors) – 41 caps
Rory Hutchinson (Northampton Saints) – uncapped
Huw Jones (Glasgow Warriors) – 21 caps
Sam Johnson (Glasgow Warriors) – 4 caps
Blair Kinghorn (Edinburgh) – 11 caps
Greig Laidlaw (Clermont Auvergne) – 71 caps
Sean Maitland (Saracens) – 40 caps
Byron McGuigan (Sale Sharks) – 8 caps
Ali Price (Glasgow Warriors) – 24 caps
Henry Pyrgos (Edinburgh) – 27 caps
Finn Russell (Racing 92) – 44 caps
Tommy Seymour (Glasgow Warriors) – 50 caps
Duncan Taylor (Saracens) – 21 caps
(Reporting by Shrivathsa Sridhar in Bengaluru, editing by Pritha Sarkar)
