GLOSSARY 393 



Ovoviviparous (o' vo vi vip' a rus). Producing young from eggs that are retained in 

 the oviduct during their development, but without attachment to the oviduct, 

 and wholly from nutrition stored in the egg. 



Ovum. An egg; a relatively large passive cell which, in preparation for reproduction, 

 has undergone one or two unequal divisions. 



Oxidation. The chemical process of combining with oxygen. 



Paedogenesis (pr' do jen' c sis). Sexual maturity in an animal otherwise immature; 

 the capability possessed by some species of reproducing wliile in the larval con- 

 dition. 



Palaeomastodon (pa' le o mas' to don). A genus of extinct animals belonging to the 

 clej)hant ancestry, found in the Oligocene of Egypt and India. 



Paleontology. The science wliich treats of prehistoric life on the earth, now repre- 

 sented by fossils. 



Paleozoic (pa' le o zo' ik). Pertaining to the geological era prior to the Mesozoic, 

 when amphibia, fishes, and the higher shell-bearing invertebrates were the domi- 

 nant forms. 



Pancreas. A gland which secretes a fluid containing several digestive enzymes and 

 discharges into the intestine. 



Pandorina. A genus of colonial flagellate organisms in which the cells are held in 

 a spheroidal jellylike mass. P. monim (trio' rum) is one of the species. 



Paramecium. A genus of ciliated protozoa. 



Parasite. An animal which lives in or on another species of animal (its host), at the 

 expense of the latter. 



Parasitism. The condition of being a parasite. 



Parathyroid. One of a pair (or two pairs) of small ductless glands closely associated 

 with the thyroid. 



Parietal bone. One of a pair of bones on the posterior upper part of the skull of 

 vertebrate animals. 



Parthenogenesis (par' the no jen' e sis). The development of an egg without fertiU- 

 zation. 



Parthenogonidia (par' the no go nid' i a). The asexually reproducing cells of Volvox. 



Paternal. Pertaining to or derived from the father. 



Pectoral girdle. A group of connected bones serving to attach the bones of the fore- 

 limbs of vertebrate animals to the rest of the skeleton. 



Peking man. An early hvmian type somewhat resembling the Piltdown and Neander- 

 thal types, found in China. 



Pelecypoda (pel' e sip' o da). A class of Mollusca having bivalve shells and a bilobed 

 mantle; the clams and mussels. 



Pellagra (pel la' gra). A condition of malnutrition accompanied by eruption of the 

 skin. 



Pellicle. A thin skin or film on the surface of a cell. 



Pelvic girdle. A group of bones serving to join the bones of the hind limbs of verte- 

 brate animals to the rest of the skeleton. 



Penis. The copulatory organ in the male of many animals. 



Pennsylvanian. The sixth period of the Paleozoic era, following the Mississippian 

 and preceding the Permian. 



Pentadactyl (pen' ta dak' til). Having five fingers or toes. 



Pepsin. An enzyme of the stomach of vertebrate animals, whose function is digestion 

 of many kinds of protein. ' 



Pepsinogen (pep sin' n jen). An inactive substance from which the enzyme pepsin is 

 derived. 



