GLOSSARY 201 



Ovipositor: the organ by means of which certain insects deposit their 



eggs, 8. 



Ovoid gland: the axial organ in the starfish, 138; in the sea urchin, 144. 

 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, 85 ; clam, 95. 

 Pallial sinus : the indentation in the pallial line, caused by the insertion of 



the siphonal retractor muscle, 95. 

 Palp : a sensory organ near the mouth ; wasp, 2 ; grasshopper, 1 1 ; crayfish 



or lobster, 28 ; Nereis, 56 ; mussel, 86 ; clam, 96. 

 Pancreas : a digestive gland in the squid, 120. 



Papulae: the delicate projections of the body-wall in the starfish, 132. 

 Paragnatha : delicate lamellae just behind the mandibles in the crayfish or 



lobster, 24. 



Paramylum: a granular substance resembling starch in Euglena, 173. 

 Parapodium : the appendage of annelids, 57. 

 Parasite: an animal which attaches itself to another and lives upon its 



nutritive fluids, 74. 

 Parenchyma: a vesicular connective tissue which fills the body-cavity of 



flatworms and leeches ; planarians, 73 ; tapeworm, 75. 

 Parthenogenesis: reproduction by means of unfertilized eggs, 51. 

 Pedicellarise : minute pincer-like organs present on the external surface of 



starfishes, 132; sea urchins, 140. 

 Pen: the shell of the squid, 115. 

 Pericardium: the membrane surrounding the heart; crayfish or lobster, 32; 



mussel, 86; clam, 97; snail, 106; Molgula, 127. 



Periopods : those thoracic appendages posterior to the maxillipeds in crusta- 

 ceans, 27. 

 Periostracum : the outer layer of the molluscan shell ; mussel, 85 ; clam, 



95 ; snail, 105. 



Periphery: the outer surface of a body. 

 Periproct: the region immediately around the anus, 140. 

 Perisarc: the cuticular outer covering of a hydroid ; tubularian, 152 ; cam- 



panularian, 156. 



Peristome: a membrane surrounding the mouth in echinoderms ; star- 

 fish, 133 ; sea urchin, 139. 

 Peristomium: the posterior portion of the head in most annelids, 



consisting of the metastomium and the anterior somites of the 



metasoma, 56. 



