I recently visited the Old Operating Theatre museum and, aside from a fantastically detailed and troubling account of Edwardian & Victorian operating theatre practices, this artefact caught my eye. It was a fairly stomach churning couple of hours ;-)
So look at this: a wonderful marriage of marketing & product design, way before these were concepts the general public might bandy about in conversation.
A little desktop research confirmed what I was thinking: these worm cakes were chocolate flavoured to make them more palatable to children, who were the intended recipients of this de-worming treatment.
Not forgetting the all important budget holding audience – the parents – who may have gained a faint hope that chocolate worm cakes would go down with less of a fight than the alternative.
An important thing to mention on the packaging, then, along with “readily taken by children” as seen on the Museum of London exhibit linked above, to press the message home.
If you feel the need, a modern equivalent is available.