Philip Belcher points out that the “correct” Latin pronunciation of ‘difficile’ is [di’fɪkɪleɪ]. He is right – for Classical Latin. The letter C was always pronounced [k]. However, the way in which English developed through the centuries meant that gradually the pronunciation of Latin words that were frequently used in English changed at the same time, and in the same way, so that C before AE, E, I, OE or Y came to be pronounced [s] – Caesar, Cicero, coeliac, Cymbeline. I don’t imagine for a second that Philip is suggesting we should go back to the Classical Latin pronunciations of these words. I’m sure that at no point did the English think they were moving away from the Latin pronunciation – just as they did not realise that their pronunciation of English words was changing at the same time.
Scientific terms – particularly the specific names of plants and animals – have generally been pronounced according to the traditional English development of Latin pronunciation – V as [v] rather than [w], AE as [i:], not [aɪ], and C as [s] or [k] depending on the following vowel (even /ʃ/ in some cases – prima facie /ˈpraɪmə ˈfeɪʃi/ comes to mind). Therefore, the Latin word DIFFICILE becomes [di’fɪsɪli], just as facsimile is pronounced [fæk’sɪmɪli].