GLOSSARY. 591 



NOTOPODIUM (Gr. notos, the back ; and nous, the foot). The dorsal division of 

 one of the foot-tubercles or parapodia of an Annelide ; often called the 

 "dorsal oar." 



NUCLEATED. Possessing a nucleus or central particle. 



NUCLEOLUS. 1. The minute solid particle in the interior of the nucleus of 

 some cells. 2. The minute spherical particle attached to the exterior of 

 the "nucleus," or ovary, of certain Infusoria, performing the functions of 

 a testicle. 



NUCLEUS (Lat. nucleus, a kernel). 1. The solid or vesicular body found in 

 many cells. 2. The solid rod, or band-shaped body, found in the interior 

 of many of the Protozoa, and having, in certain of them, the functions of an 

 ovary. 3. The " madreporiform tubercle " of the Echinodermata. 4. The 

 embryonic shell which is retained to form the apex of the adult shell in 

 many of the Mollusca. 



NUDIBRANCHIATA (Lat. nudus, naked ; and Gr. Iragchia, gill). An order of 

 the Gasteropoda in which the gills are naked. 



NYMPHS. The active pupae of certain Insects. 



OCCIPITAL. Connected with the occiput, or the back part of the head. 



OCEANIC. Applied to animals which inhabit the open ocean ( = pelagic). 



OCELLI (Lat. diminutive of oculus, eye). The simple eyes of many Echino- 

 derms, Spiders, Crustaceans, Molluscs, &c. 



OCTOPODA (Gr. octo, eight; pous, foot). The tribe of Cuttle-fishes with eight 

 arms attached to the head. 



ODONTOCETI (Gr. odous, tooth; ketos, whale). The "toothed" Whales, in 

 contradistinction to the * ' whalebone " Whales. 



ODONTOID (Gr. odous ; eidos, form). The " odontoid process " is the centrum 

 or body of the first cerviaal vertebra (atlas). It is detached from the atlas, 

 and is usually anchylosed with the second cervical vertebra (axis), and it 

 forms the pivot upon which the head rotates. 



ODONTOPHORE (Gr. odous, tooth ; phero, I carry). The so-called "tongue," 

 or masticatory apparatus of Gasteropoda, Pteropoda, and Cephalopoda. 



(ESOPHAGUS. The gullet or tube leading from the mouth to the stomach. 



OLIGOCH^TA (Gr. oliyos, few; chaite, hair). An order of Annelida, compris- 

 ing the Earth-worms, in which there are few bristles. 



OMASUM (Lat. bullock's tripe). The third stomach of Ruminants, commonly 

 called the psalterium, or many-plies. 



OMNIVOROUS (Lat. omnia, everything ; voro, I devour). Feeding indiscrimin- 

 ately upon all sorts of food. 



OPERCULATA (Lat. operculum, a lid). A division of pulmonate Gasteropoda, 

 in which the shell is closed by an operculum. 



OPERCULUM. A horny or shelly plate developed in certain Mollusca upon the 

 hinder part of the foot, and serving to close the aperture of the shell when 

 the animal is retracted within it ; also the lid of the shell of a Balanus or 

 Acorn-shell ; also the chain of flat bones which cover the gills in many 



OPHIDIA (Gr. ophis, a serpent). The order of Reptiles comprising the Snakes. 

 OPHLDOBATRACHIA (Gr. ophis; latrachos, a frog). Sometimes applied to the 



order of Snake-like amphibians comprising the Ccecilioe. 

 OPHIOMORPHA (Gr. ophis; morphe, shape). The order of Amphibia com prising 



the Ccecilice. 

 OPHIUROIDEA (Gr. ophis, snake ; oiira, tail ; eidos, form). An order of Echin- 



odermata, comprising the Brittle-stars and Sand-stars. 

 OPISTHOBRANCHIATA (Gr. opistlien, behind ; bragchia, gill). A division of 



Gasteropoda, in which the gills are placed on the posterior part of the body. 

 OPISTHOCCELOUS (Gr. opisthen, behind ; koilos, hollow). Applied to vertebrae, 



the bodies of which are hollow or concave behind. 

 ORAL (Lat. os, mouth). Connected with the mouth. 

 ORNITHODELPHIA (Gr. ornis, a bird ; delphus, womb). The primary division 



of Mammals comprising the Monotremata. 

 ORTHOPTERA (Gr. orthos, straight ; pteron, wing). An order of Insects. 



