The reflexes of the proto-Bantu noun class prefixes of the form "mu-,""mi-," and "ma-" are compared in 84 Bantu languages. The hypotheses that syllabic nasals arise preferably from sequences of m + rounded high vowel, rather than m + unrounded high vowel, are tested against the data. The approach is an example of intragenetic comparison discussed by Greenberg (1969). The results confirm the hypotheses. Some details on the stages of development of syllabic nasals are discussed, and a formal representation of the intermediate states and processes is sketched. (Author)