GLOSSARY 235 



Giant fibers: three large fibers in the dorsal portion of the nerve cord in 



the earthworm. 

 Gill : an organ for the breathing of air contained in the water. 

 Gill filament: ciliated vertical ridges on the surface of the gills. 

 Gizzard: a portion of the alimentary tract with thickened muscular walls; 



a chewing stomach. 

 Gland: an organ which produces a secretion. 

 Glochidium: the larval form of Anodonta and Unio, which lives a parasitic 



life in the skin of fishes. 

 Glottis: the opening from the pharynx into the trachea. 

 Gonotheca: the cuticular outer covering of the blastostyle. 

 Green gland: the kidney of a malacostracan crustacean. 



Haemal: pertaining to the blood system. 



Head: the anterior body division of the higher animals. 



Heart: a muscular tubelike or saclike organ which propels the blood. 



Hermaphroditic: having the two sexes united in one animal. 



Hinge ligament: the flexible portion of a bivalve shell which joins the 

 two valves. 



Homologous: having had a similar origin. 



Host: the animal which harbors a parasite. 



Hydranth: a feeding polyp in a hydroid colony. 



Hydrocaulus : the stem of a hydroid colony. 



Hydroid: the sessile, asexual generation of the Hydromedusae. 



Hydrorhiza: the rootlike projections of a hydroid colony by which it is 

 attached. 



Hydrotheca: the cuticular outer covering of the hydranth in campanularian 

 hydroids. 



Hypodermis: the cellular layer which forms the inner portion of the integu- 

 ment of most invertebrates. 



Hypopharynx: a median projection from the ventral wall of the pharynx 

 in insects. 



Hypophysis: a ventral projection of the brain in vertebrates. 



Hypostome: the projection of a hydroid's body which bears the mouth. 



Imago: an insect which has completed its metamorphosis ; an adult insect. 



Incurrent: passing inward. 



Integument: the outer covering of an animal. 



Interfilamentary connections: cross ridges which join the gill filaments in 



clams. 

 Interlamellar partitions: vertical walls which join the two lamellae of a 



clam's gills. 

 Intermediate host: the animal which harbors the larval form of a parasite. 

 Interray: one of the divisions of the radiate body of echinoderms. 

 Intestine: a division of the digestive tract. 



