486 GLOSSARY. 



the order of the Leeches (Hirudmea) , from the suctorial discs which these 

 animals possess. 



DissEPiMEXTS (Lat. dissejno, I partition off). Partitions. Used in a restricted 

 sense to designate certain imperfect transverse partitions, which grow from 

 the sejjta of many corals. 



Distal. Applied to the quickly -growing end of the hj'drosoma of a Hydrozoon ; 

 the opposite, or "proximal," extremity growing less rapidly, and being the 

 end hy which the organism is fixed, when attached at all. Applied generally 

 to that extremity of a limb, muscle, or bone, which is furthest removed 

 from the trunk. 



DiURXAL (Lat. dies, day). Applied to animals which are active during the 

 day. 



Dorsal (Lat. dorsum, back). Connected with the back. 



DoRSiBRANCHiATE (Lat. dorsum, the back ; Gr. bragchia, gill). Having ex- 

 ternal gills attached to the back ; applied to certain Annelides and Molluscs. 

 The term is of mongrel composition, and " notobranchiate " is more cor- 

 rectly employed. 



EcHiNODEKMATA (Gr. cchhios ; and derma, skin). A class of animals com- 

 jirising the Sea-urchins, Star-fishes, and others, most of which have spin)' 

 skins. 



ECHINOIDEA (Gr. cehinos ; and cidos, form). An order of Ediinodcrmata, 

 comprising the Sea-urchins. 



EcHiNULATE. Possessing spines. 



EcTOCYST (Gr. ektos, outside ; hustis, a bladder). The external investment of 

 the coenoecium of a Poli/zodti. 



Ectoderm (Gr. ektos; and derma, skin). The external integumentary layer of 

 the Ccelenterata. 



Edentata (Lat. e, without ; dens, tooth). An order of Mammalia often 

 called Bruta. 



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 wliich the eyes are sessile, and are not supported upon 

 stalks. 



Elasmobranchii (Gr. elas7na, a plate ; bragchia, gill). An order of Fishes, 

 including the Sharks and Rays. 



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

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

 plied to the scales or plates on the back of the Sea-mouse {Aj^hrodite). 



Embryo (Gr. c?i, in ; bruo, I swell). The earliest stage at which the young 

 animal is recognisable in the impregnated ovum. 



EN.A.LIOSAURIA (Gr. cnalios, marine ; saura, lizard). Sometimes employed as 

 a common term to designate the extinct Reptilian orders of the Ichthyosauria 

 and Plesiosauria. 



Encephalous (Gr. en, in ; kephalc, the head). Possessing a distinct head. 

 Usuallj' applied to all the Mollnsca proper, except the Lamellibranchiata. 



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

 tegumentary layer of a Polyzoon. In Cristatella, where there is no "ecto- 

 cyst," the endocyst constitutes the entire integument. 



