found on reddit

Generations of anything are 'supposed' to be based on function not design.

The usual thought is that cigalikes are 1st gen, pen vapes are 2nd, and mods are 3rd as shown here : http://i.imgur.com/xksOsk5.jpg

But this is both chronologically, and functionally incorrect.

This infographic is far more accurate : http://i.imgur.com/p7gLt6B.png