582 GLOSSARY. 



EDENTULOUS. Toothless, without any dental apparatus. Applied to the 

 mouth of any animal, or to the hinge of the bivalve Molluscs. 



EDRIOPHTHALMATA (Gr. hedraios, sitting; ophthalmos, eye). The division of 

 Crustacea in which the eyes are sessile, and are not supported upon stalks. 



ELASMOBRANCHII (Gr. elasma, a plate ; bragchia, gill). An order of Fishes, 

 including the Sharks and Rays. 



ELYTRA (Gr. elutron, a sheath). The chitinous anterior pair of wings in 

 Beetles, which form cases for the posterior membranous wings. Also ap- 

 plied to the scales or plates on the back of the Sea-mouse (A phrodite). 



EMBRYO (Gr. en, in ; bi~uo, I swell). The earliest stage at which the young 

 animal is recognisable in the impregnated ovum. 



ENCEPHALON (Gr. eycephalos, brain). The portion of the cerebro-spinal ner- 

 vous axis contained within the cranium. 



ENCEPHALOUS (Gr. en, in ; kephale, the head). Possessing a distinct head. 



Usually applied to all the Mollusca proper, except the Lamellibranchiata. 



ENCYSTATION (Gr. en, in ; kustis, a bag). The transformation undergone by 

 certain of the Protozoa, when they become motionless, and surround them- 

 selves by a thick coating or cyst. 



ENDERON (Gr. en, in ; deros, skin). The inner plane of growth of the outer 

 integumentary layer (viz., the ectoderm, or epidermis). 



ENDOCYST (Gr. endon, within; kustis, a bag). The inner membrane or integu- 

 mentary layer of a Polyzob'n. In Cristatella, where there is no " ectocyst," 

 the endocyst constitutes the entire integument. 



ENDODERM (Gr. endon; and derma, skin). The inner integumentary layer of 

 the Ccelenterata. 



ENDOPODITE (Gr. endon; and pous, foot). The inner of the two secondary 

 joints into which the typical limb of a Crustacean is divided. 



ENDOSARC (Gr. endon; and sarx, flesh). The inner molecular layer of sarcode 

 in the Amoeba, and other allied Rhizopods. 



ENDOSKELETON (Gr. endon, and skeletos, dry). The internal hard structures, 

 such as bones, which serve for the attachment of muscles, or the protection 

 of organs, and which are not a mere hardening of the integument. 



ENSLFORM (Lat. ensis, a sword ; forma, shape). Sword-shaped. 



ENTOMOPHAGA (Gr. entoma, insects ; phago, I eat). A section of the Marsu- 

 pialia. 



ENTOMOSTRACA (Gr. entoma, insects ; ostrakon, a shell). Literally Shelled 

 Insects, applied to a division of Crustacea. 



ENTOZOA (Gr. entos, within ; zob'n, animal). Animals which are parasitic in 

 the interior of other animals. 



EOCENE (Gr. eos, dawn ; kainos, new or recent). The lowest division of the 

 Tertiary Rocks, in which species of existing shells are to a small extent 

 represented. 



EPIDERMIS (Gr. epi, upon ; derma, the true skin). The outer non-vascular 

 layer of the skin, often called the scarf-skin or cuticle. 



EPIMERA (Gr. epi, upon ; meron, thigh). The lateral pieces of the dorsal arc 

 of the somite of a Crustacean. 



EPIPODIA (Gr. epi, upon ; pous, the foot). Muscular lobes developed from 

 the lateral and upper surfaces of the " foot " of some Molluscs. 



EPIPODITE (Gr. epi, upon ; pous, foot). A process developed upon the basal 

 joint, or " protopodite," of some of the limbs of certain Crustacea. 



EPISTERNA (Gr. epi, upon ; sternon, the breast-bone). The lateral pieces of 

 the inferior or ventral arc of the somite of a Crustacean. 



EPISTOME (Gr. epi; and stoma, mouth). A valve-like organ which arches over 

 the mouth in certain of the Polyzoa. 



EPITHECA (Gr. epi; and theke, a sheath). A continuous layer surrounding the 

 thecse in some Corals, and being the external indications of tabulae. 



EPIZOA (Gr. epi, upon ; zob'n, animal). Animals which are parasitic upon 

 other animals. In a restricted sense, a division of Crustacea which are 

 parasitic upon fishes. 



EQUILATERAL (Lat. (equus, equal ; latus, side). Having its sides equal. Us- 

 ually applied to the shells of the Brachiopoda. When applied to the spiral 



