240 GLOSSARY 



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. 



PINNAE. The smaller branches of a branching structure. 



PINNULES. The smallest branches of a branching structure. 



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. 



PROTEID. Term used here in the sense of protein; The American Society of 

 Biological Chemists and the American Physiological Society have 

 recommended that the term 'proteid' be abandoned. 



PROTEIN. That group of chemical substances which consist essentially of 

 amino acids and their derivatives. 



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. 



PROTOPODITE. The first or basal division of an appendage of a crustacean. 



PSEUDOPODIUM. A temporary prolongation or protrusion of the proto- 

 plasm of amoeboid cells. 



RECEPTOR. The molecule in protoplasm with which a toxin or various 

 metabolic elements may unite. 



RECESSIVE. In heredity, a factor which, although present in a hetero- 

 zygous individual, remains undeveloped. 



REDUCTION. The halving of the number of chromosomes in the nucleus of 

 a germ cell during maturation. 



REGIONAL DIFFERENTIATION. Specialization of a part of the body not 

 duplicated in other parts. 



RHIZOID. Resembling a root. 



RHIZOME. An underground trunk or stem. 



ROTIFER. Minute multicellular animal with rings of powerful cilia; "wheel- 

 animalcule." 



SAPROPHYTIC. Food-taking by absorption or osmosis; applies to some 

 plant forms. 



SAPROZOIC. Same, applying to animal forms. 



SCOLEX. The " head " or attaching segment of a tape- worm. 



SEX-LINKED. Any character the factor of which is associated with the sex 

 determiner. 



SINUS. A cavity or hollow in tissues.. 



