5^4 



GLOSSARY 



underlies the central nervous system of a 

 Vertebrate embryo, and may persist throug-h- 

 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 



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 e\'L'. 



Ocular (L. ociilus, an e^c), bearing" eyes, e.g. 

 the ocular plates in the apical disc of a 

 sea-urchin. 



Odontophore (Gk. adous, oduiitos, a tooth ; 

 phi^ro, I bear), the rasping" organ in tht 

 mouth-cavity of Snails, Cuttle-Fishes, <S:c. 



CEsophagus, the gullet. 



Omasum, in the stomach of Ruminants, the 

 third compartment. 



Omnivorous, of mixed diet. 



Ontogeny (Gk. aula, beings; gt^utiao, I pro- 

 duce), the development of individual animals. 



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

 g"ill-cover of (L Fish; (2) the horn-\- or shellv 

 plate with which the opening of the shell 

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

 Scorpions, Kiiig-Crabs, &:c., :i plate on the 

 under side ot the bod\', immediateh' behind 

 the last pair ot legs; (4) the plug \vith which 

 some tube-dwelling Aimelids can close the 

 openings of their tubes. 



Opisthobranch (Gk. o/^is/Zu'', behind; /^nn/r/na, 

 g-ills), applied to Sea-Snails with gills behind 

 the heart. 



Oral {L. (Js, the mouth), relating to the mouth. 



Oral papillae, in Peripatus, a pair of stump- 

 like limbs near the mouth, upon which the 

 slime-glands open. 



Orbit, the cavlt\- of the skull in which the eye- 

 ball is lodged. 



Organic selection, the co-operation of Accom- 

 modation and Ad^iptation (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 ot water lea\'e 

 the body. 



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

 odour), a sense-organ which probably tests 

 the nature of the water entering the gih- 

 cavity of aquatic Molluscs. 

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

 regular bone. Auditory ossicles, in drum of 

 ear. 

 Otocyst (Gk. <ius, otns^ an ear ; rj's//'s, a 

 bladder), a minute vesicle of sensor}" nature, 



containing one or more hard particles. Pro- 

 bably a balancing organ. 



Otolith (Gk. oi{Sf otds, an ear; lith^Sy a stone), 

 a firm particle within an otocyst or internal 

 auditory organ. 



Ovary, an organ producing egg-cells. 



Oviparous (L. ovuiii^ an g^^ ; 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. oi ovum, an ^%%)-, 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 ^%%), an egg-cell, the 

 earliest stage in the development of an 

 embryo. 



Oyster-park, an enclosed area of shallow 

 water in which o}'sters are grown. 



Pacinian corpuscle, a minute o\oid laminated 

 bod}', connected with 's. sensor\' ner\e, and 

 probably having to do with the pressure- 

 sense. 



Palas arctic region {G\i. palaius, ancient; arktuSy 

 the north), the northern part of the old 

 world. 



Palaeolithic period (Gk. palaids, ancient; 

 lithuSy a stone), the earlier stages of the 

 Stone Age. 



Palasozoic epoch (Gk. palaios, 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. paluia, a hand), divided like a 

 hand. 



Palp (L. paJpo, 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. parOy 

 b}' the side of; /)ous, pudos, a foot): (i) 

 in Bristle-Worms, c)ne 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. pa/-asilus, a svcophant), an 

 organism which lives on (ectoparasite) or in 

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

 feeding' on its juices, substiince, or dlg'ested 

 food. 



Parasitism {Gk. paraslius^ a sycophant), the 

 association of a parasite with a " host ", the 



