Marsupials, the. ova of the. Materialism. Mathematical method, the. Mechanical causes. embryology. Meckel's cartilage. Medulla capitis, the. oblongata, the. spinalis, the. Medullary groove, the. tube, the. formation of the. Mehnert, E., on the biogenetic law. Meroblastic ova. Merocytes. Mesentery, the. Mesocardium, the. Mesoderm, the. Mesogastria. Mesonephridia, the. Mesonephros, the. Mesorchium, the. Mesovarium, the. Mesozoic period, the. Metogaster, the. Metagastrula, the. Metamerism. Metanephridia, the. Metanephros, the. Metaplasm. Metastoma. Metatheria. Metazoa. Metovum, the. Microgonidian. Microspores. Middle ear, the. Migration, effect of. Milk, secretion of the. Mind, evolution of. in the lower animals. Miocene strata. Mitosis. Monera. Monism. Monodelphia. Monogonopora. Monopneumones. Monotremes. ova of the. Monoxenia Darwinii. Morea, the. Morphology. Morula, the. Motor-germinative layer, the. Mouth, development of the. structure of the. Mucous layer, the. Mullerian duct, the. Muscle-layer, the. Muscles, evolution of the. of the ear, rudimentary. Myotomes. Myxinoides, the. Nails, evolution of the. Nasal pits. Natural philosophy. selection. Navel, the. Necrolemurs. Nectocystis, the. Nemertina. Nephroduct, evolution of the. Nephrotomes. Nerve-cell, the. Nerves, animals without. Nervous system, evolution of the. Neurenteric canal, the. Nictitating membrane, the. Nose, the, in man and the ape. development of the. structure of the. Notochorda, the. Nuclein. Nucleolinus. Nucleolus, the. Nucleus of the cell. Oesophagus, the. Oken. Oken's bodies. Oligocene strata. Olynthus. On the generation of animals. Ontogeny. defective evidence of. Opaque area, the. Opossum, the. ova of the. Optic nerve, the. Optic thalami. vesicles. Orang, the. Ornithodelphia. Ornithorhyncus. Ornithostoma. Ossicles of the ear. Otoliths. Ova, number of. of the lancelet. Ovaries, evolution of the. Oviduct, origin of the. Ovolemma, the. Ovulists. Ovum, discovery of the. nature of the. size of the. Pachylemurs, the. Pacinian corpuscles. Paleontology. evolutionary evidence of. incompleteness of. rise of. Paleozoic age, the. Palingenesis. Palingenetic structures. Palaehatteria. Panniculus carnosus, the. Paradidymis, the. Parietal zone, the. Parthenogenesis. Pastrana, Miss Julia. Pedimana. Pellucid area, the. Pelvic cavity, the. Pemmatodiscus gastrulaceus. Penis-bone, the. Penis, varieties of the. Peramelida. Periblastic ova. Peribranchial cavity, the. Pericardial cavity, the. Perichorda, the. formation of the. Perigastrula. Permian strata. Petromyzontes, the. Phagocytes. Pharyngeal ganglion, the. Pharynx, the. Philology, comparison with. Philosophie Zoologique. Philosophy and evolution. Phycochromacea. Phylogeny. Physemaria. Physiology, backwardness of. Phytomonera. Pineal eye, the. Pinna, the. Pithecanthropus. Pithecometra-principle, the.