I don't quite understand the phrase "More than a million boys’ periodicals were sold a week" - it seems to mean "More than a million copies of the penny dreadfuls (periodicals) subscribed by boys were sold a week." I am not sure at all.
What does the phrase mean?
The penny dreadfuls were printed on cheap wood pulp paper and were aimed at young working class men.[4] More than a million boys’ periodicals were sold a week, but the popularity of penny dreadfuls was challenged in the 1890s by the rise of competing literature, especially the half-penny periodicals published by Alfred Harmsworth.[3][5]
Source: Wiki