200 INVERTEBRATE ZOOLOGY 



Nerve commissure: a nerve connecting the two members of a pair of 



ganglia; planarian, 72; tapeworm, 76; mussel, 91; clam, 101; snail, 



111. 

 Nerve connective : a nerve connecting two ganglia not of the same pair ; 



grasshopper, 17; crayfish or lobster, 35; Nereis, 59; mussel, 91; 



clam, 101. 



Nettle cell: the stinging organ in the Cnidaria; Hydra, 145. 

 Neuropodium: the ventral division of the parapodium of an annelid, 57. 

 Nidamental glands : the large glands which secrete the egg-capsules in the 



squid, 123. 



Notopodium: the dorsal division of the parapodium of an annelid, 57. 

 Nucleus : a spheroidal body in a cell, the center of its activities ; Parame- 



cium, 166; Vorticella, 170; Euglena, 173; Amoeba, 175. 



Ocellus: a minute primitive eye; wasp, 2 ; grasshopper, 7; caterpillar, 18 ; 



tubularian medusa, 154. 



Ocular plate: the plate at the aboral end of a ray of the sea urchin, 141. 

 (Esophagus : the gullet, the division of the digestive canal leading from the 



pharynx to the stomach; grasshopper, 13; caterpillar, 19; crayfish or 



lobster, 33 ; Nereis, 58 ; earthworm, 65 ; Bugula, 80 ; mussel, 90 ; 



clam, 100; snail, 107; squid, 121; Molgula, 127; starfish, 135; sea 



urchin, 141. 



Ommatidium : a single element of the compound eye of an arthropod. 

 Ocecium: a structure in Bryozoa in which the embryo develops, 81. 

 Oral : the side of the body containing the mouth in a radiate animal ; star- 

 fish, 132; sea urchin, 139; medusa, 153, 159. 



Oral groove: a groove leading to the mouth in ciliate infusorians, 164, 168. 

 Organ of Keber: an organ probably excretory in function in lamellibranchs ; 



mussel, 86 ; clam, 97. 



Osculum: the cloacal opening in sponges, 161. 

 Ossicles: the calcareous plates in the body-wall of echinoderms. 

 Otocyst: an organ of hearing ; mussel, 92 ; clam, 101. 

 Ovarioles : the tubules forming the ovary of an insect, 14. 

 Ovary: the female sexual gland ; grasshopper, 14 ; crayfish or lobster, 33 ; 



crab, 38; copepod, 49; Daphnia, 51; earthworm, 66; planarian, 71; 



tapeworm, 77; mussel, 91; clam, 100; squid, 123; starfish, 136; 



Hydra, 147. 

 Oviduct : the tube leading from the ovary towards the outside ; grasshopper, 



14 ; crayfish or lobster, 33 ; crab, 38 ; copepod, 49 ; Daphnia, 51 ; 



earthworm, 66; planarian, 71; snail, 110; squid, 123. 



