300 MANUAL OF ZOOLOGY. 



HYDROTHECA (Gr. kudra ; and thekc, a case). The little chitinous cups in 

 which the polypi tes of the Surtularida and Campanularida are protected. 



HYDROZOA (Gr. hudra ; and zobn, animal). The class of the Coelenterata, 

 -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. 



HYPOSTOME (Gr. hupo, under ; stoma, mouth). The upper lip, or ' labrum ' 

 of certain Crustacea (e.g. Trilobites). 



ICHTHYOPHTHIRA (Gr. ichthus, fish ; phtheir, a louse). An order of Crus- 

 tacea, comprising animals which are parasitic upon fishes. 



IMAGO (Lat. an image, or apparition). The perfect insect, after it has 

 undergone its metamorphosis. 



IMBRICATED. Applied to scales or plates which overlap one another like 

 tiles. 



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 Foraminiftra, it implies that the convolutions of the shell do 

 not lie in the same plane, but are obliquely wound round an axis. . 



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. 



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

 monate Gasteropoda in which there is no shelly or horny plate (oper- 

 culum) by which the shell is closed when the animal is withdrawn with- 

 in it. 



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

 known as Insects. 



INTERAMBULACRA. The rows of plates in an Echinoderm, which are not 

 perforated for the emission of the 'tube-feet.' 



INTUSSUSCEPTION (Lat. intus, within ; suscipio, I take up). The act of 

 taking foreign matter into a living being. 



INVERTEBRATA (Lat. in, without; vertebra, a bone of the back). Animals 

 without a spinal column or backbone. 



ISOPODA (Gr. isos, eqxial ; poda, feet). An order of Crustacea in which the 

 feet are like one another and equal. 



KAINOZOIC (Gr. Jcainos, recent ; zoe, life). The Tertiary period in Geology, 



comprising those formations in which the organic remains approximate 



more or less closely to the existing fauna and flora. 

 KERATODE (Gr. Jceras, horn; eidos, form). The horny substance of which 



the skeleton of many sponges is made up. 

 KERATOSA. The division of Sponges in which the skeleton is composed of 



keratode. 



LABIUM (Lat. for lip). Restricted to the lower lip of Articulate animals. 



LABRUM (Lat. for lip). Restricted to the upper lip of Articulate animals. 



L.:MODIPODA (Gr. laima, throat ; dis, twice ; poda, feet). An order of 

 Crustacea, so called because they have two feet placed far forwards, as 

 it were under the throat. 



LAMELLIBRANCHIATA (Lat. lamella, a plate, Gr. bragchia, gill). The class of 

 Mollusca, comprising the ordinary bivalves, characterised by the posses- 

 sion of lamellar gills. 



