GLOSSARY 217 
Osculum : the cloacal opening in sponges, 181. 
Ossicles: the calcareous plates in the body-wall of echinoderms. 
Otocyst : an organ of hearing; mussel, 98; clam, 111. 
Ovarioles: the tubules forming the ovary of an insect, 16. 
Ovary: the female sexual gland; grasshopper, 16; spider, 27; crayfish or 
lobster, 37; crab, 44; copepod, 55; Daphnia, 57; earthworm, 72; pla- 
narian, 77; tapeworm, 83; mussel, 97; oyster, 102; clam, 110; squid, 
183; starfish, 146; Hydra, 161. 
Oviduct : the tube leading from the ovary towards the outside; grasshopper, 
16; spider, 27; crayfish or lobster, 89; crab, 44; copepod, 55; Daph- 
nia, 57; earthworm, 72; planarian, 77; snail, 120; squid, 133. 
Ovipositor: the organ by means of which certain insects deposit their eggs; 
fly, 8; grasshopper, 10. 
Ovoid gland: the axial organ in the starfish, 148; in the sea urchin, 154. 
Ovum: the female sexual cell, the egg. ° 
Pallial line: the line along which the margin of the mantle is attached to 
the shell in lamellibranchs; mussel, 91; clam, 195. 
Pallial sinus: the indentation in the pallial line caused by the insertion of 
the siphonal retractor muscle, 105. 
Palp: a sensory organ near the mouth; wasp, 2; grasshopper, 13; crayfish 
or lobster, 34; Nereis, 62; mussel, 92; oyster, 101; clam, 106. 
Pancreas; a digestive gland in the squid, 130. 
Papule: the delicate projections of the body-wall in the starfish, 142. 
Paragnatha: delicate lamelle just behind the mandibles in the crayfish 
or lobster, 30. 
Paramylum: a granular substance resembling starch in Euglena, 193. 
Parapodium: the appendage of annelids, 63. 
Parasite: an animal which attaches itself to another and lives upon its 
nutritive fluids, 80. 
Parenchyma: a vesicular connective tissue which fills the body-cavity of 
flatworms and leeches; planarians, 79; tapeworm, 81. 
Parthenogenesis : reproduction by means of unfertilized eggs, 58. 
Pedicellarie: minute pincer-like organs present on the external surface 
of starfishes, 142; sea urchins, 150. 
Pedipalps: the second pair of appendages in the Arachnida, 24. 
Pen: the shell of the squid, 125. 
Pericardium : the membrane surrounding the heart; spider, 26; crayfish 
or lobster, 38; mussel, 92; oyster, 101; clam, 107; snail, 115; Molgula, 
137. 
