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, 

 133 ; starfish, 146 ; Hydra, 161. 



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

 16 ; spider, 27 ; crayfish or lobster, 39 ; 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. 



Papulae : the delicate projections of the body-wall in the starfish, 142. 

 Paragnatha : delicate lamellae 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. 

 Pedicellariae : 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. 



