Medullation of nerve-fibres, [20], [267], [467], [477]
Membranes, basement, [436]
Meroblastic egg, [485]
Merostomata, [25], [249], [321]
Mesencepalon, [48]
Mesoblast, [444], [455], [459]
Mesoglœa, [474]
Mesonephros, [389], [400], [424], [429]
Mesosoma, [52]