GLOSSARY 



507 



Radial symmetry. See Sy?nvieiry. 



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 stagfcs 

 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. -3e (after the Italian naturalist 

 R€di\ in Flukes, a cylindrical stag-e in the 

 life-history, produced by the Sporocyst (which 

 see). 



Reed. See Abomasmn. 



Regeneration, the power of repairing- injuries. 



Rejuvenescence (L. rejuvenesco, I become 

 young ag^ain), the invig^oration produced b}' 

 nuclear fusion. See Fertilization. 



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

 wing". 



Rennet stomach. See Aho7?iasum. 



Rennin, a milk-curdling- ferment contained in 

 gastric juice. 



Resemblance, General, a harmonizing: with 

 surrounding-s producing- inconspicuousness. 

 It may be protective, ag-g-ressive, or both. 

 When capable of adjustment it is said to be 

 variable. 



Resemblance, Special, a resemblance to some 

 specific object in the surroundings, by w^hich 

 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: draw^n back. 



Reversion, the appearance of characters un- 

 like those of the preceding: g-eneration, but 

 resembling- those of remoter ancestors. 



Rhabdites (Gk. rhabdSs, 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. rhopalon^ a club), in 

 some Jelly-fishes, a specialized club-shaped 

 tentacle bearing- various sense-org-ans. 



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. mniinatioy 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-g-irdles) of the hind- 

 limbs. 



Saliva (the Latin name), spittle. 



Salivary gland, a g:land 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 toug:h exter- 

 nal coat of the eyeball. 



Sebaceous (L. sebum, g-rease), of a g:reasy or 

 oily nature. 



Secondary: (i) acquired within the limits of a 

 ^roup; (2) replacing- some earHer structure. 



Segmentation: (i) the division of the adult 

 body into successive rings, segments, or 

 somites; (2) the early stages of division in 

 the eg-g-cell. 



Self-fertilization, fertilization of an eg-g:-cell 

 by a sperm (or its equivalent) derived from 

 the same org-anlsm. 



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 g-round. 



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

 set (calyx) of investing: flower-leaves. 



Sessile (L. sessi/is, sitting), without a stalk. 



Seta, pi. -as (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 nitrog-en- 

 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 g-ill 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- 



