Mastobranchus, gill of, [268], [331]
Matzdorf, on Leeches, [369]
Maupas, on Rotifers, [217]
Mbalolo, [297]
Meckelia asulcata, [111]
Mecynostoma, [49]
Median pore, in Cheilostomata, [484], [524]
Megadrili, [373], [374], [380] f.
Megalotrocha, [221]
Megapora, [530]