384 PRINCIPLES OF ANIMAL BIOLOGY 



Hydropsyche Qii' dro si' kee). A genus of insects including certain caddis-flies. 



Hydrorhiza (hi' dro ri' za). That part of a hydroid colony which is attached to the 



sub-stratum. 

 Hydrotaxis {hi' dro tak' sis). A response to moisture. 



HydrOtheca(/a'' dro the' ka). The tough transparent sheath surrounding a hydranth 

 of a hydroid ; an expansion of the perisarc. 



Hydrotropism {hi drot' ro piz'm). The response of an organism to water, or moisture. 



Hydrozoa {hi' dro zo' a). A class of Ccelenterata, including Hydra, the hydroids, 

 jellyfishes, and some corals. For definition see Chapter XII. 



Hyla {hi' la). A genus of tree frogs. 



Hymenoptera {hi' men op' ter a). An order of insects, embracing the bees, ants> 

 wasps, iclmeumon fhes, and others. 



Hyoid {hi' oid). A bone or group of bones or cartilages located at the base of the 



tongue or in a corresponding situation. 

 Hypertonicity {hi' per to nis' i ti) . The presence of a greater osmotic pressure than 



normal ; for example, in sea water. 

 Hypodermis {hi' po der' mis). An external layer of cells beneath a secreted cuticle, 



as in the earthworm and in insects and Crustacea. 



Hypohippus (hi' po hip' pus). An extinct horse-Uke animal of Miocene time in 



North America. 

 Hypostome {hi' po stome). A projection from the center of the circle of tentacles 



in Hj'dra or one of the hydroids. It is perforated by the mouth. 



flypotonicity {hi' po to nis' i ti). The presence of a lower osmotic pressure than 

 normal ; for example, in sea water. 



Ichneumon fly {ik nu' mon). One of a family of parasitic insects of the order Hymen 

 optera. 



Qeum {iV e um). The last and usually longest of three divisions of the small intestine. 



Ilium (iV i um) (pi., ilia). The dorsal bone of the pelvic girdle in Amphibia and the 

 higher vertebrates. 



Incisor {in si' zer). One of the front cutting teeth of a mammal. 



Incubation {ing' ku ha' shun). The warming of eggs, resulting in acceleration of their 

 development. 



Infusoria {in' fu zo' ri a). A class of Protozoa members of which are covered with a 

 pellicle, have a fixed mouth, and are usually covered with cilia ; example, Parame- 

 cium. 



Ingestion {in jes' chun). The taking in of food. 



Inhalent {in hn' lent). Breathing in; applied to one of the siphons of clams and 

 mussels, to certain pores of sponges, and to other passages. 



Innominate bone {innom' inate). The single bone formed by the fusion of three 

 bones of the pelvic girdle in man. This name is not usually applied in the case 

 of other vertebrates, though fusion of the bones of the girdle commonly occurs. 



Insecta {in sek' to). A class of Arthropoda having one pair of antennae, throe pairs of 

 legs, and tracheae for respiration , the insects. 



Insectivore {in sek' ti vore). Technically, a mammal of the order Insectivora, including 

 the moles, shrews, and hedgehogs. In a popular sense, any insect-eating animal. 



Interalveolar {in' ter al ve' o ler). Existing between the alveoli; said of the supporting 

 liquid of an emulsion, in which the alveoli are enclosed. 



