Appendix 853 



Prothallus (pro -thai' us) (Gr. pro, before; thallos, young part), the reduced pre- 

 thallus gametophyte of ferns and their alHes. 



Prothorax (pro -thor' aks) {pro, before; thorax, chest), anterior segment of insect 

 thorax which bears first pair of legs. 



Protista (pro -tis' ta) (Gr. protistos, first), single-celled plants and animals. 



Proton (pro'ton) (Gr. protos, first), part of a nucleus of the atom, and with a 

 positive charge of electricity. 



Protonema (pro to -ne' ma) (Gr. proto, first; nema, thread), first threadlike 

 growth from a spore in mosses. 



Protoplasm (pro' to plazm) (Gr. protos, first; plasma, liquid), substance of which 

 all living organisms are composed. 



Protopodite (pro -top' o dite) (Gr. protos, first; pons, foot), basal (proximal) seg- 

 ment of a typical crustacean appendage to which endopodite and exopodite 

 are attached. 



Protozoan (pro to -zo' an) (Gr. protos, first; zoa, animals), simple, unicellular 

 animals. 



Proventriculus (pro ven -trik' u lus) (Gr. pro, before; ventriculus, small stomach), 

 first part of a stomach in such animals as insects, birds, etc. 



Proximal (prox' i mal) (L. proximus, near), nearest the main axis; opposed to 

 distal. 



Pseudopodium (plural, pseudopodia) (su do -po' di um) (L. pseudo, false; pous, 

 feet), temporary protrusion of protoplasm from a cell, especially certain 

 protozoa like ameba, and serving for various functions but particularly 

 locomotion. 



Psychical (si' kik al) (Gr. psyche, soul), pertaining to .the mind. 



Psychology (si -kol' o ji) (Gr. psyche, mind; logos, study), study of the mind, etc. 



Pteropsida (ter -op' si da) (Gr. pteris, fern; opsis, appearance), a subphylum to 

 which ferns, conifers, and flowering plants belong. 



Ptomaine (to' mane) (Gr. ptoma, dead body), an organic base or alkaloid formed 

 by the action of putrefactive bacteria on nitrogenous matter. Some pto- 

 maines are poisonous but most are harmless. 



Ptyalin (ty' a lin) (Gr. ptyalon, spittle), salivary enzyme changing starch to sugar. 



Pubis (pu'bis) (L. pubes, adult), anterior part of the hip (pelvic) girdle. 



Pulmonary (pul' mon a ri) (L. pulmo, lung), pertaining to the lung. 



Pulsating vacuole, same as Contractile vacuole. 



Punnet square, a checkerboard-like diagram for determining the results of a 

 cross in heredity. 



Pupa (pu'pa) (L. pupa, baby), the quiet stage in the development of certain 

 insects occurring between the larval and adult stages; known as a cocoon in 

 moths and chrysalis in butterflies. 



Pure line, a group of individuals arising from homozygous parents and having 

 identical genes. 



Pylorus (pi-lo'rus) (Gr. pylorus, gate), opening between stomach and small in- 

 testine. 



Pyrenoid (pi -re' noid) (Gr. pyren, fruit stone; eidos, resembling), plastid or cen- 

 ter for forming starch. 



