GLOSSARY 



507 



Radial symmetry. See Symmetry. 



Radius: (i) (L. radius, a ray), in radially sym- 

 metrical animals, one of the axes of sym- 

 metry which radiate from a central point, as 

 the spokes of a wheel do from the hub ; (2) 

 (the Latin meaning), the bone of the fore- 

 arm which is on the thumb-side. 



Radula (L. radula, a scraper), the horny 

 tooth-studded ribbon that constitutes the 

 rasping- part of the Odontophore (which 

 see). 



Raphides (Gk. rhaphis, -idos, a needle), in 

 plants, bundles of needle-shaped crystals of 

 oxalate of lime. 



Ratite (L. rates, a raft): (i) shaped like a raft, 

 i.e. devoid of a keel-like projection; (2) ap- 

 plied to running birds, in which the breast- 

 bone is so shaped. 



Recapitulation, repetition of ancestral stages 

 in the life-history. 



Recognition-markings, in Birds and Mam- 

 mals, colour-arrangements which aid in 

 rapid recognition by members of the same 

 species. 



Rectrices (L. for female rulers), quill-feathers 

 of the tail. 



Redia, pi. -ae (after the Italian naturalist 

 Redi\ in Flukes, a cylindrical stage in the 

 life-history, produced by the Sporocyst (which 

 see). 



Reed. See Abomasum. 



Regeneration, the power of repairing injuries. 



Rejuvenescence (L. rejuvenesco, I become 

 young again), the invigoration produced by 

 nuclear fusion. See Fertilization. 



Remiges (L. for rowers), quill-feathers of the 

 wing. 



Rennet stomach. See Abomasum. 



Rennin, a milk-curdling ferment contained in 

 gastric juice. 



Resemblance, General, a harmonizing with 

 surroundings producing inconspicuousness. 

 It may be protective, aggressive, or both. 

 When capable of adjustment it is said to be 

 variable. 



Resemblance, Special, a resemblance to some 

 specific object in the surroundings, by which 

 inconspicuousness is produced. It may be 

 protective, aggressive, or both. When 

 capable of adjustment it is said to be 

 variable. 



Reticulum (L. for a little net), in the stomach 

 of Ruminants, the second compartment. 



Retina (L. rete, a net), the sensitive internal 

 layer of the eye. 



Retinaculum (L. for a rope or bond), in 

 Moths, a tuft of scales or flap on the posterior 

 part of the fore-wing. The Frenulum (which 

 see) interlocks with it. 



Retractile (L. retractum, drawn back), ca- 

 pable of being drawn back. 



Reversion, the appearance of characters un- 

 like those of the preceding generation, but 

 resembling those of remoter ancestors. 



Rhabdites (Gk. rhabdb's, a rod), in Planarian 



Worms (Turbellaria), microscopic rods dis- 

 charged from the skin as a means of defence 

 and probably of irritant nature. 



Rhopalion, pi. -a (Gk. rhtipaltiny a club), in 

 some Jelly-fishes, a specialized club-shaped 

 tentacle bearing various sense-organs. 



Rods and Cones, the sensitive cells of the eye 

 in Vertebrates. 



Rostellum (L. for little beak), a sticky knob 

 connected with the pollinia of an orchid. 



Rudimentary organ. See Vestige. 



Rumen (L. ruminatio, chewing the cud), in the 

 stomach of Ruminants, the first compart- 

 ment. 



Rumination (L. ruminatio), chewing the cud. 



Sacrum, in the backbone, the part connected 

 with the supports (hip-girdles) of the hind- 

 limbs. 



Saliva (the Latin name), spittle. 



Salivary gland, a gland which secretes or 

 elaborates saliva (spittle). 



Scaly epithelium, epithelium composed of flat 

 cells. 



Scapula (the Latin name), the shoulder-blade. 



Sclerotic (Gk. skleros, hard), the tough exter- 

 nal coat of the eyeball. 



Sebaceous (L. sebum, grease), of a greasy or 

 oily nature. 



Secondary: (i) acquired within the limits of a 

 group; (2) replacing some earlier structure. 



Segmentation: (i) the division of the adult 

 body into successive rings, segments, or 

 somites; (2) the early stages of division in 

 the egg-cell. 



Self-fertilization, fertilization of an egg-cell 

 by a sperm (or its equivalent) derived from 

 the same organism. 



Self-pollination, transfer of pollen to the 

 stigma of a flower from its own stamens. 



Semi-plantigrade, with palms and soles partly 

 resting on the ground. 



Sepal (Gk. sk&pe, a covering), one of the outer 

 set (calyx) of investing flower-leaves. 



Sessile (L. sessilis, sitting), without a stalk. 



Seta, pi. -ae (the Latin name), a bristle. 



Shagreen, the skins of certain Sharks and 

 Dog - Fishes, containing numerous hard 

 scales. 



Shell-cameos, carvings made on certain shells 

 which are composed of differently coloured 

 layers. 



Shell-gland, in lower Crustaceans, one of a 

 pair of excretory organs removing nitrogen- 

 ous waste from the body. They open at the 

 bases of the third jaws (2nd maxillae). 



Shell-muscle, the muscle by which a snail is 

 attached to its shell. 



Shoulder-girdle, skeleton of shoulder. 



Side-gill, in Crustaceans, a gill attached to 

 the side of the body. 



Signalling coloration, conspicuous patches of 

 colour, e.g. the white tail of a Rabbit, dis- 

 played during rapid movement. The ap- 



