802 GLOSSARY. 



HYDROIDA (Gr. hudra; and eidos, fonn). The sub-class of the Hydrozoa, 

 which comprises the animals most nearly allied to the Hydra. 



HYDROPHYLLIA (Gr. hudra; and phullon, a leaf). Overlapping appendages 

 or plates which protect the pplypites in some of the oceanic Hydrozoa, 

 (Calycophorida and Physophoridce). They are often termed " bracts," and 

 are the " Deckstiicke" of the Germans. 



HYDBORHIZA (Gr. hudra ; and rhiza, root). The adherent base or proximal 

 extremity of any Hydrozoon. 



HYDROSOMA (Gr. hudra ; and soma, body). The entire organism of any 

 Hydrozoon. 



HYDROTHECA (Gr. hudra; and theke, a case). The little chitinous cup in 

 which the polypites of the Sertularida and Campanulas ida are protected. 



HYDROZOA (Gr. hixlra; and zoon, animal). The class of the Ctelenterata, 

 which comprises animals constructed after the type of the Hydra. 



HYMENOPTERA (Gr. humen, a membrane ; pteron, a wing). An order of In- 

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

 membranous wings. 



HYOID (Gr. U ; eidos, form). The bone which supports the tongue in Verte- 

 brates, 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). 



HYRACOIDEA (Gr. hurax, a shrew ; eidos, form). An order of the Mammalia 

 constituted for the reception of the single genus Hyrax. 



ICHTHYODORULITE (Gr. ichthus, fish ; dorus, spear ; lithos, stone). The fossil 

 fin-spines of Fishes. 



ICHTHYOMORPHA (Gr. ichthus ; morphe, shape). An order of Amphibians, 

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



ICHTHYOPHTHIRA (Gr. ichthus ; phtheir, a louse). An order of Crustacea com- 

 prising animals which are parasitic upon Fishes. 



ICHTHYOPSIDA (Gr. ichthus ; opsis, appearance). The primary division of 

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

 Branchiate Vertebrata. 



ICHTHYOPTERYGIA (Gr. ichthus ; pterux, 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. 



INCISOR (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 (Lamellibranchiata). When applied to the shells 

 of the Foraminifera, 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." 



INFUSORIA (Lat. infusum, an infusion). A class of Protozoa, so called be- 

 cause they are often developed in organic infusions. 



INGUINAL (Lat. inguen, groin). Connected with, or situated upon, the groin. 



INOPERCULATA (Lat. in, without ; operculum, a lid). The division of pul- 

 monate Gasteropoda in which there is no shelly or horny plate (operculum) 

 by which the shell is closed when the animal is withdrawn within it. 



INSECTA (Lat. inseco, I cut into). The class of Articulate animals commonly 

 known as Insects. 



INSECTIVORA (Lat. insectum, an insect ; voro, I devour). An order of Mammals, 



INSECTIVOROUS. Living upon Insects. 



