GLOSSARY 239 



METAMERISM. Segmentation of the body along the main axis, resulting in 

 a series of more or less similar parts which are serially homologous. 



MICRONUCLEUS. The smaller nucleus of an infusorian in which dimorphic 

 nuclei are present. 



MICROSOMES. The minute granules embedded in the ground substance of 

 protoplasm. 



MIMICRY. The simulation of something else in form or color, usually 

 having protective value to an organism. 



MITOSIS. The processes involved in nuclear division, including formation 

 and division of the chromosomes. Same as karyokinesis. 



MORPHOLOGY. The science which deals with form. 



MUTATION. The process of originating a new species or a new specific char- 

 acter at a single step; discontinuous variation. 



NEMATOBLAST. A nettle thread-forming cell of Hydra and allied forms. 



NEMATODE. A round- or thread-worm. 



NEPHRIDIUM. The excretory organ of invertebrate animals. 



NEPHROBLAST. Initial cell of a chain of cells in development destined to 

 form an excretory organ or part thereof. 



NEPHROSTOME. Mouth or internal opening of a nephridium. 



NEUROBLAST. Initial cell in a chain of cells in development destined to form 

 the nervous system or part thereof. 



NEURON. Morphological and physiological unit of the nervous system con- 

 sisting of a nerve cell, its nucleus, axon, and dendrites. 



NUCLEUS. A differentiated portion of the cell protoplasm consisting of mem- 

 brane, chromatin, linin, nucleoli and ground substance. 



OMMATIDIUM. A radial element or segment of the compound eye of an ar- 

 thropod. 



ONTOGENY. The developmental history of a given organism as distinguished 

 from phylogeny or history of the race. 



OOGENESIS. The development of the ovum from a primordial sex cell. 



OTOCYST. A vesicle associated with the sense of equilibration in lower 

 animals; a primitive auditory organ. 



OTOLITH. A mineral element or concretion in an auditory vesicle. 



OXIDATION. The action or process of taking up or combining with oxygen. 



PARENCHYMA. The fundamental cellular tissue of plants. 



PARTHENOGENESIS. Development without fertilization of an egg into a 

 normal individual. 



PERICARDIUM. The membrane around the heart. 



PERISTALSIS. Wave-like involuntary contraction of circular muscles of a 

 tubular organ. 



PERISTOME. The region around the mouth. 



PHAGOCYTE. Amoeboid cells of the blood able to engulf other cells or 

 foreign objects. 



PHAGOCYTOSIS. The process of engulfing by a phagocyte or white blood cell. 



PHOTOSYNTHESIS. The process by which green plants utilize the energy 

 of sunlight in the manufacture of starch. 



