296 MANUAL OP ZOOLOGY. 



Molluscs. The term is of mongrel composition, and ' notobranchiate ' is 

 more correctly employed. 



ECDERON (Gr. ek, out; derns, skin). The outer plane of growth of the ex- 

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

 ECDYSIS (Gr. ekdusis, a stripping off). A shedding or moulting of the skin. 

 ECHIXOCOCCI (Gr. echinos, a hedge-hog ; kokkos, a berry). The larval forms 



(Scolices) of the tapeworm of the dog (Tcenia echinococcus], commonly 



known as ' hydatids.' 



ECHINODERMATA (Gr. echinos ; and derma, skin). A class of animals com- 

 prising the Sea-urchins, Star-fishes and others, most of which have spiny 



skins. 

 ECHINOIDEA (Gr. echinos; and eidos, form). An order of Echinodermata, 



comprising the Sea-urchins. 

 ECHINULATE. Possessing spines. 

 ECTOCYST (Gr. ektos, outside ; kustis, a bladder). The external investment 



of the coencecium of a Polyzobn. 

 ECTODERM (Gr. ektos, and derma, skin). The external integumentary layer 



of the Ccelenterata. 

 ECTOSARC (Gr. ektos ; and sarx, flesh). The outer transparent sarcode-jayer 



of certain Bhizopods, such as the Amceba. 

 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. 

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



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



applied to the scales or plates on the back of the Sea-mouse (Aphrodite}. 

 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 



themselves 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 Polyzoon. In Cristatella, where there is no ' ectocyst,' 



the endoeyst constitutes the entire integument. 

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



of the Codenterata. 

 ENDOPODITE (Gr. endon ; and pons, 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 Bhizopods. 

 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. 

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

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



Insects ; applied to a division of Crustacea. 

 ENTOZOA (Gr. entos, within ; zoon, 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, 



