506 APPENDIX 



Paleontology. The science of extinct animals and plants represented 

 by fossil remains. 



Parapodium. Locomotor and respiratory organ of marine worms; e.g., 

 Nereis. 



Parasite. An organism which secures its livelihood directly at the ex- 

 pense of another living organism, on or in whose body it lives. 



Parazoa. Animals without an enteron or coelom. Sponges. 



Parthenogenesis. Development of an egg without fertilization. 



Pathogenic. Disease-producing, especially in regard to the relation of 

 a parasite to its host. 



Pentadactyl. Having five fingers or toes; typical Vertebrate limb. 



Pericardium. Peritoneum lining the pericardial cavity containing the 

 heart. 



Periosteum. Connective tissue sheath covering bone and contributing 

 to its growth. 



Peristalsis. Rhythmical contractions of the wall of the alimentary canal 

 which force the food along. 



Peritoneum. Membrane lining coelom of Vertebrates. Mesodermal in 

 origin. 



Pharynx. Region of alimentary canal between buccal cavity, or mouth, 

 and esophagus. Throat. 



Phenotype. The somatic, or expressed, characters of an organism or 

 group of organisms irrespective of those potential in their germ cells. 

 See Genotype. 



Photosynthesis. Process by which complex compounds are built up from 

 simple elements through the energy of sunlight absorbed by chlorophyll. 



Phylogeny. The ancestral history of the race. See Ontogeny. 



Phylum. In classification, a main subdivision of the animal kingdom. 

 See Class. 



Physiology. The study of the functions of animals and plants. The 

 mechanical and chemical engineering of organisms. 



Pineal Body. An outgrowth from the upper wall of the diencephalon. 

 The vestige of an additional eye possessed by the ancestors of existing 

 Vertebrates. Possibly functions as an endocrine gland in Mammals. 

 Brow-spot of Frog. 



Pituitary Gland. A glandular body under the brain, formed of tissue 

 from the nervous system and from the alimentary canal. Secretes 

 several hormones. 



Placenta. A Mammalian organ adapted for the interchange of all nu- 

 tritive, respiratory, and excretory materials between the embryo (fetus) 

 and mother. It also serves as an organ of attachment. In the higher 

 Mammals it is composed of both fetal and maternal tissues. See Um- 

 bilical Cord. 



