450 APPENDIX 



RESTING CELL. One which is not undergoing mitosis. 



RETINA. Actual percipient part of the eye by virtue of a sensory 

 layer which is stimulated by light rays. 



REVERSION. The appearance of a distant ancestral character in an 

 individual. See Atavism. 



RHIZOID. A root-like filament in lower plants; e.g., in Mosses and 

 prothallus of Ferns. 



RHIZOME. Prostrate underground stem; e.g., in sporophyte of com- 

 mon Ferns. 



ROOT HAIRS. Prolongations of epidermal cells just above the grow- 

 ing point of roots which afford surface for intake of water and 

 solutes. 



ROSTRUM. The anterior pointed extension of the exoskeleton of the 

 Crayfish and its allies. 



ROTIFERA. Microscopic, aquatic, multicellular animals. Wheel 

 animalcules. 



RUSTS. Fungi which are destructive parasites of the higher plants; 

 e.g., the Wheat Rust. 



SACCULUS. The anterior sac of the labyrinth of the ear, a derivative 

 of which becomes the cochlea in higher Vertebrates. 



SAPROPHYTIC. Type of nutrition involving the absorption of com- 

 plex products of organic decomposition; e.g., in many groups of 

 Bacteria and other Fungi, as well as various species of lower 

 animals. See Holozoic and Holophytic. 



SEBACEOUS GLANDS. Glands which elaborate a fatty substance 

 (sebum) and secrete it in the hair follicles. 



SECRETION. A substance elaborated by glandular epithelium; or 

 the process involved. See Gland and Excretion. 



SEED. An embryo sporophyte supplied with food and protective 

 envelopes. 



SEGREGATION. The distribution of contrasting genes (allelomorphs) 

 to separate cells during the maturation of the germ cells in a 

 heterozygous individual (hybrid). 



SEMICIRCULAR CANALS. Portion of the Vertebrate ear devoted to 

 equilibrium. 



SEMINAL RECEPTACLES. Globular sacs within the body cavity of 



