Appendix 849 



Pedogenesis, see Paedogenesis. 



Pellicle (pel'ikl) (L. pellicula, small skin), thin layer as on certain cells. 



Pelvis (pel' vis) (L. pelvis, basin), arrangement of bones to support abdominal 

 organs and for attachment of lower (hind) limbs. 



Penis (pe' nis) (L. penis, penis), male organ of copulation. 



Pentadactyl (pen ta -dak' til) (Gr. penta, five; daktylos, finger), five fingers or 

 digits. 



Pepsin (pep' sin) (Gr. pepsis, digest), protein-digesting enzyme of the stomach. 



Perennial (per-en'ial) (L. per, through; annus, year), plant living more than 

 two years (contrast with Annual and Biennial). 



Perianth (per'ianth) (Gr. peri, around; anthos, flower), all the petals and 

 sepals of a flower taken collectively. 



Pericardium (per i -kar' di um) (Gr. peri, around; kardia, heart), serous mem- 

 bane which encloses the heart. 



Pericycle (per' i si kl) (Gr. peri, around; kyklos, circle), circle of plant tissue of 

 stems and roots between the cortex and stele. 



Perimysium (peri -mizh' i um) (Gr. peri, around; mys, muscle), covering or bind- 

 ing muscle. 



Periosteum (peri -os' te um) (Gr. peri, around; os, bone), membranous connective 

 tissue that covers bones. 



Peripheral nervous system, that part of the nervous system composed of cranial and 

 spinal nerves (contrast with Central nervous system). 



Peristalsis (per i -stal' sis) (Gr. peri, around; stallein, to arrange), wavelike con- 

 striction passing along a tube, due to muscular contraction, as in esopha- 

 gus, intestine, etc. 



Peritoneum (per i to -ne' um) (Gr. peri, around; teinein, to stretch), membrane 

 which lines the coelom of vertebrates and covers the viscera of the coelom. 



Permeable membrane, one which permits substances to pass. 



Perspiration (per spi -ra' shun) (L. per, through; spiro, to breathe), watery ex- 

 cretion of perspiratory glands of skin. 



Petal (pet' al) (Gr. petalon, leaf), one of the inner whorl of a flower, usually 

 colored; all petals taken collectively form the corolla. 



Petiole (pet'iol) (L. petiolus, little stalk), slender support for the blade of a 

 foliage leaf. 



Petrifaction (pet ri -fak' shun) (L. petra, rock), method of fossil formation in 

 which mineral matter takes the place of the original organic or living 

 matter during the disintegration of the organism. 



Peyer's patches (after Swiss anatomist, Peyer), oval patches of lymphoid tissue 

 of the small intestine attacked by typhoid germs in man. 



Phaeophyta (fe -of i ta) (Gr. phaeo, brown; phyta, plants), brown algae. 



Phagocyte (fag' o site) (Gr. phagein, eat; kytos, cell), type of leucocyte which 

 engulfs foreign materials. 



Phagocytosis (fag o si -to' sis), destruction of foreign materials by action of 

 phagocytes (white blood corpuscles). 



Pharyngeal cleft, see Gill slit. 



Pharynx (far' inks) (Gr. pharynx, pharynx), tube connecting mouth to esopha- 

 gus on the one hand and to the larynx on the other. 



