244 GLOSSARY 



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. 

 PARABASAL BODY. A part of the kinetic complex of a flagellated protozoan. 

 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 cell 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. 

 PHYLOGENY That branch of biology which treats of the ancestral history 



of animals or plants. 



PHYLUM. Any primary group in the animal or vegetable kingdom. 

 PHYTOL. A primary alcohol composing part of the chlorophyll molecule. 

 PINN/E. The smaller branches of a branching structure. 

 PINNULES. The smallest branches of a branching structure. 

 PLASMODIUM The cause of malaria, a protozoan. 



POLAR BODY. A minute abortive cell given off by an ovum during matura- 

 tion. 

 POLYMORPHISM. Capacity of an animal or plant to exist under different 



forms or types. 

 PROCTODAEUM. The posterior part of the digestive tract of an animal 



formed by the ingrowth of ectoderm. 



PROGLOTTID. One of the posterior segments of a tape- worm. 

 PROSTOMIUM. The lobe in front of or overhanging the mouth of an annelid. 

 PROTEASE. An enzyme capable of transforming proteins into diffusible 



bodies. 

 PROTEIN. That group of chemical substances which consist essentially of 



amino acids and their derivatives. 



PROTEOLYTIC. Capable of breaking down, or dissolving, protein. 

 PROTEOSE A secondary protein derivative. 

 PROTHALLIUM. Sexual generation derived by germination of the spore in 



the higher cryptogams and bearing the sexual organs. 

 PROTONEMA. Outgrowth from the germinating spore in higher cryptogams, 



which develops into the prothallium. 

 PROTOPLASM. The living substance of animals and plants. 



