490 GLOSSARY. 



Homologous (Gr. homos; and logos, a discourse). Applied to parts which 

 are constructed upon the same fundamental plan. 



Humerus. Tlie bone of the upper arm {brackium) in the Vertebrates. 



Hyaline (Gr. hualos, crystal). Cr3'stalline or glassy. 



Htbodonts (Gr. huhos, curved; odous, tooth). A group of Fishes of which 

 Hyhodiis is the type-genus. 



Hydro IDA (Gr. hudra ; and cidos, form). The sub-class of the Hydrozoa, 

 which comprises the animals most nearly allied to the Hydra. 



Hydrotheca (Gr. Imdra ; and tlieke, a case). The little chitinous cups in 

 which the polj^pites of the Scrtularida and Campamdarkla are protected. 



Hydrozoa (Gr. hudra; and zoon, animal). The class of the Coslenterata 

 which comprises animals constructed after the type of the Hydra. 



Hymexoptera (Gr. humeri, a membrane ; pteron, a wing). An order of In- 

 sects (comprising, Bees, Ants, &c.) characterised by the possession of four 

 membranous wings. 



Hyoid (Gr. U ; cidos, form). The bone which supports the tongue in Ver- 

 tebrates, and derives its name from its resemblance in man to the Greek 

 letter U. 



Hypostome (Gr. hupo, under ; stoma, mouth). The upper lip, or " labrum," 

 of certain Crustacea {e.g., Trilobites). 



Hy'RACOIdea (Gr. hurax, a shrew ; cidos, form). An order of the Mammalia 

 constituted for the reception of the single genus Hyrax. 



Ichthyodorulite (Gr. ichthus, fish ; dorus, spear ; lUhos, stone). The fossil 

 fin-spines of Fishes. 



Ichthyomorpha (Gr. ichthus ; Tnorphc, shape). An order of Amphibians, 

 often called Urodela, comprising the fish-like Newts, &c. 



Ichthy'ophthira (Gr. ichthus ; pihthcir, a louse). An order of Crustacea com- 

 prising animals which are parasitic upon Fishes. 



Ichthyopsida (Gr. ichthus; apsis, appearance). The primary division of 

 Vertehrata, comprising the Fishes and Amphibia. Often spoken of as the 

 Branchiate Vertebrata. 



Ichthyopterygia (Gr. ichthus ; piterux, wing). An extinct order of Reptiles. 



IcHTHYOSAURiA (Gr. ichthus ; saura, lizard. Synonymous with Ichthyo- 

 pterygia. 



Ilium. The haunch-bone, one of the bones of the pelvic arch in the higher 

 Vertebrates. 



Imago (Lat. an image or apparition). The perfect insect, after it has under- 

 gone its metamorphoses. 



Imbricated. Applied to scales or plates which overlap one another like tiles. 



Ikcisor (Lat. incido, I cut). The cutting teeth fixed in the intermaxillary 

 bones of the Mammalia, and the corresponding teeth in the lower jaw. 



Inequilateral. Having the two sides unequal, as in the case of the shells 

 of the ordinary Bivalves {Lamcllibranchiata). When applied to the shells 

 of the Foraviinifera , it implies that the convolutions of the shell do not lie 

 in the same plane, but are obliquely wound round an axis. 



Inequivalve. Composed of two unequal pieces or valves. 



Infundibulum (Lat. for funnel). The tube formed by the coalescence or 

 apposition of the epipodia in the Cephalopoda. Commonly termed the 

 "funnel," or "siphon." 



