GLOSSARY 



underlies the central nervous system of a 

 Vertebrate embryo, and may persist through- 

 out life. Usually more or less replaced by 

 the backbone, of which it is the forerunner. 



Nuchal (L. nucha, neck), relating- to the neck. 



Nucleus (L. for a kernel), a specialized par- 

 ticle of protoplasm within a cell. 



Nymph, in Insects with incomplete metamor- 

 phosis, the stage which hatches from the 

 egg- 



Oceanic island, an island that has never 

 formed part of any existing continent. 



Ocellus, pi. -i, (L. for a little eye), in Arthro- 

 pods, a small simple eye. 



Ocular (L. oculus, an eye), bearing eyes, e.g. 

 the ocular plates in the apical disc of a 

 sea-urchin. 



Odontophore (Gk. tidous, b'do'nfo's, a tooth; 

 phVro, I bear), the rasping organ in the 

 mouth-cavity of Snails, Cuttle-Fishes, &c. 



Oesophagus, the gullet. 



Omasum, in the stomach of Ruminants, the 

 third compartment. 



Omnivorous, of mixed diet. 



Ontogeny (Gk. tfnta, beings; g&nnao, I pro- 

 duce), the development of individual animals. 



Operculum, pi. -a (L. for lid or cover): (i) the 

 gill-cover of a Fish ; (2) the horny or shelly 

 plate with which the opening of the shell 

 can be closed in some Sea-snails ; (3) in 

 Scorpions, King-Crabs, &c., a plate on the 

 under side of the body, immediately behind 

 the last pair of legs ; (4) the plug with which 

 some tube-dwelling Annelids can close the 

 openings of their tubes. 



Opisthobranch (Gk. tipisthe', behind; branchia, 

 gills), applied to Sea-Snails with gills behind 

 the heart. 



Oral (L. os, the mouth), relating to the mouth. 



Oral papillae, in Peripatus, a pair of stump- 

 like limbs near the mouth, upon which the 

 slime-glands operv. 



Orbit, the cavity of the skull in which the eye- 

 ball is lodged. 



Organic selection, the co-operation of Accom- 

 modation and Adaptation (which see) in the 

 production of new species. 



Oriental region, south Asia, with the adjacent 

 part of the East Indies, the Philippines, and 

 Formosa. 



Origin of a muscle, the end attached to a 

 relatively fixed part. 



Osculum (L. for a little mouth), in Sponges, 

 an opening by which currents of water leave 

 the body. 



Osphradium, pi. -ia (dim. of Gk. tisphra, an 

 odour), a sense-organ which probably tests 

 the nature of the water entering the gill- 

 cavity of aquatic Molluscs. 



Ossicle (L. dim. of efc, a bone), a small ir- 

 regular bone. Auditory ossicles, in drum of 

 ear. 



Otocyst (Gk. ous, ottis, an ear; cystis, a 

 bladder), a minute vesicle of sensory nature, 



containing one or more hard particles. Pro- 

 bably a balancing organ. 



Otolith (Gk. ous, otos, an ear ; lithtis, a stone), 

 a firm particle within an otocyst or internal 

 auditory organ. 



Ovary, an organ producing egg-cells. 



Oviparous (L. ovum, an egg; pario, I produce), 



egg-laying. 



Ovipositor, in Insects, a piercing arrange- 

 ment at the hinder end of the body in the 

 female, for making holes in plants, &c., 

 and introducing eggs into them. 



Ovule $L. dim. of ovum, an egg), in Flowering 

 Plants, the small body which becomes a seed 

 after the egg-cell it contains has been fer- 

 tilized. 



Ovum, pi. -a (L. for an egg), an egg-cell, the 

 earliest stage in the development of an 

 embryo. 



Oyster-park, an enclosed area of shallow 

 water in which oysters are grown. 



Pacinian corpuscle, a minute ovoid laminated 

 body, connected with a sensory nerve, and 

 probably having to do with the pressure- 

 sense. 



Palaearctic region (Gk. palaio's, ancient; arktos, 

 the north), the northern part of the old 

 world. 



Palaeolithic period (Gk. palaibs, ancient; 

 lithbs, a stone), the earlier stages of the 

 Stone Age. 



Palaeozoic epoch (Gk. palaitis, ancient; zoe, 

 life), the most ancient geological era but one. 



Pallial line, in Bivalve Molluscs, a mark on 

 the inner side of each valve, corresponding 

 to the attachment of the mantle or pallium. 



Pallium (L. for a cloak). See Mantle. 



Palmated (L. palma, a hand), divided like a 

 hand. 



Palp (L. palpo, I touch gently), a sensitive 

 outgrowth, e.g. of some mouth-parts in 

 Insects. Labial palp, one of four sensitive 

 triangular flaps adjoining the mouth of a 

 Bivalve Mollusc. 



Pancreas (the Greek name), the sweet-bread. 

 An abdominal gland, which pours its secre- 

 tion (pancreatic juice) into the intestine. 



Pancreatic juice, the secretion of the pancreas. 

 It acts upon albuminoids, starch, and fats. 



Papilla (L. for a nipple), a small projection. 



Parapod, or Parapodium, pi. -ia (Gk. para, 

 by the side of; pans, podtis, a foot): (i) 

 in Bristle- Worms, one of the hollow conical 

 unjointed foot-stumps ; (2) in some Sea-Slugs, 

 a muscular flap arising far down on each 

 side of the foot. 



Parasite (Gk. parasitos, a sycophant), an 

 organism which lives on (ectoparasite) or in 

 (endoparasite) a larger organism ("host"), 

 reeding on its juices, substance, or digested 

 food. 



Parasitism (Gk. parasltos, a sycophant), the 

 association of a parasite with a "host", the 



