In Darwin's time, all educated people in the western world learned Latin, and many also learned classical Greek. Consequently, they had little problem handling words of Latin and Greek origin. These days, few people learn either Latin or Greek. If you learned neither Latin nor Greek, you need to learn how to pronounce scientific names (SECTION 10). You need also to recognize singular and plural forms of English words of Latin and Greek origin (SECTION 4).
Some of the words mentioned in SECTION 4 are now commonly mishandled by the general public. For example, the words agenda, algae, bacteria, data, criteria, fungi, and larvae are all PLURAL forms, of which the singular forms are agendum, alga, bacterium, datum, criterion, fungus, and larva.
It is curious that the PLURAL forms are being misused -- as if they were both singular and plural. Take the word "larva" (pl. "larvae"). Many non-biologists wrongly use the word "larvae" as both singular and plural ["a larvae", "two larvae"]. Pretty soon, someone with no knowledge of Latin will wonder what is the plural form of the word, will add the letter 's' as in most other English words, and the English language will begin to change ["larvae" as singular and "larvaes" as plural]. But there is no need to change - it all works very well by using the Latin singular and plural forms shown in section 4. And, if we MUST change, we would do better to adopt the singular and plural as used in Spanish and Portuguese (SECTION 13) instead of inventing something new.
So you think the example above is imaginative -- that it won't happen? Well, consider what already has happened. The word agendum exists, with plural agenda. But "WWWebsters" dictionary has agenda (the plural form of the word) as a main entry and suggests that "agendas" is an acceptable plural or at least that "agendas" is being used widely. See Dictionaries (Section 18).
Meanwhile, the singular and plural forms as specified in section 4 are the only ones acceptable to editors of scientific journals -- and are the only ones acceptable in your thesis or dissertation.