The author researched the following ten languages during his stay in Cameroun from September, 1990 up to February, 1991:
Kaka, Makaa, Eton, Ewondo, Bulu, Bafia, Yambasa, Bassa, Douala, Dschang.
Generally speaking, their linguistic features can be stated as below:
1) Some of these languages have implosive stops and some have double-articulated stops such as kp and gb.
2) Some of them have seven vowels (i, e, ε, a, _??_, o, u) and others have a central vowel (_??_) besides them. Some have nasalized vowels.
3) Many of them have closed syllables as well as open syllables.
4) Some of them have a phenomenon such that a high-toned syllable becomes middle-toned when it stands immediately after a high-toned syllable.
5) Some languages have very few noun classes.
6) For modification, some languages use a construction made of an adjectival noun followed by ‘of’+a concrete noun.
7) The infinitive prefixes in many languages are not those originating in *ku.
8) Some languages use personal pronouns in some cases instead of original subject prefixes.
9) The object prefixes are not used in many of them.
10) Some languages use verb stems seemingly extended by *ag (+ *a) as well as those with the ending *a.
11) The verbs are tonally divided into two groups in all of them.
Their mutual linguistic differences seem to be very large and almost all of them seem to have changed very much from Proto-Bantu although they are spoken near the so-called Bantu homeland.