GLOSSARY 197 



Hermaphroditic : having the two sexes united in one animal ; earthworm, 

 65; planarian, 71 ; tapeworm, 75 ; Bryozoa, 81 ; snail, 110; Molgula, 

 127; Hydra, 147. 



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

 valves ; mussel, 83 ; clam, 93. 



Holometabolic : insects having a complete metamorphosis. 



Homologous : having had a similar origin. 



Host : the animal which harbors a parasite, 74. 



Hydranth: an individual feeding polyp in a hydroid colony, 150, 156. 



Hydrocaulus: the stem of a hydroid colony, 150, 155. 



Hydroid: the sessile, asexual generation of the Hydromedusae, 149, 155. 



Hydrorhiza: the root-like projections of a hydroid colony by which it is 

 attached, 150, 155. 



Hydrotheca : the cuticular outer covering of the hydranth in campanularian 

 hydroids, 156. 



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

 ment of most invertebrates ; crayfish or lobster, 30 ; earthworm, 68. 



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

 insects in many insects an important mouth-part, 10. 



Hypophysis: a ventral projection of the brain in vertebrates, 128. 



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

 Hydra, 146 ; campanularian, 156. 



Ileum: a division of the intestine in insects, 13. 



Imago: a holometabolic insect which has completed its metamorphosis; 

 an adult insect. 



Integument: the outer covering of an animal; in most invertebrates it con- 

 sists of an outer cuticula and an inner hypodermis. 



Interfilamentary connections: cross-ridges which join the gill-filaments in 

 lamellibranchs ; mussel, 88; clam, 98. 



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

 lamellibranch's gill; mussel, 87; clam, 97. 



Intermediate host: the animal which harbors the larval form of a para- 

 site, 78. 



Interray : one of the divisions of the radiate body of echinoderms; starfish, 

 132 ; sea urchin, 140. 



Intestine: the division of the digestive tract in which absorption goes 

 on; crayfish or lobster, 31; copepod, 47; planarian, 71; Bugula, 80; 

 mussel, 90; clam, 100; snail, 108 ; squid, 121; Molgula, 127; starfish, 

 135 ; sea urchin, 142. 



