GLOSSARY. 667 



HYDROCAULUS (Gr. hudra, a water-serpent ; and kaulos, a stem). The main 



stem of the coe.nosarc of a Hydrozoon. 

 HYDROCYSTS (Gr. hudra ; and kustis, a cyst). Curious processes attached to 



the coenosarc of the Physnphoridce, and termed " feelers " (fuhler and taster 



of the Germans). 

 HYDRfficiUM (Gr. hudra ; and oikos, a house). The chamber into which the 



ccenosaro in many of the Calycophoridce can be retracted. 

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



which comprises the animals most nearly allied to the Hydra. 

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



or plates which protect the polypites in some of the oceanic Hydrozoa 



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



are the " deckstilcke " of the Germans. 

 HYDRORHIZA (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 cups in 



which the polypites of the Sertularida and Gampanularida are protected. 

 HYDROZOA (Gr. hudra; and zoon, animal). The class of the Ccelenterata, 



which comprises animals constructed after the type of the Hydra. 

 HYMENOPTERA (Gr. humen, 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; eidos, foi*m). 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). 

 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,sione}. 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. ickthus ; 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. 



TcHTHYOSAURlA(Gr. ichthus ; saura, lizard). Synonymous with Ichthyopterygia. 



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. 



