A comprehensive grammar of the English languageShe's studying European history 
She's studying the history of Europe. [1b]
(....) we notice a slight difference between  and [1b]: whereas [1b] implies that she is studying the history of Europe as a whole,  allows the interpretation that she is studying only some aspects of European history or a particular college course.
The type of contrast illustrated above by  and [1b] can also be noted with concrete noncount nouns, and with plural nouns:
This museum specializes in 18th century furniture. 
This museum specializes in the furniture of the 18th century. [2a]
Alice is engaged in research on South American butterflies 
Alice is engaged in research on the butterflies of South America. [3a]
But in these cases it is to a greater or lesser degree acceptable to omit the:
The museum specializes in furniture of the 18th century. [2b]
?Alice is engaged in research on butterflies of South America. [3b]
As I see, they mean that [2b] is "to a greater degree", and [3b] is "to a lesser degree". But I don't understand why. Does it have to do with furniture being noncountable, while butterflies being countable?