42 GLOSSARY. 



Echmi'dea (Gr. echinos, a sea-urchin, hedge-hog). The sea- 

 urchins. 

 EcMnoder'mata (Gr. echinos, a hedge-hog; derma, skin). A 



division of the Invertebrata which includes the sea- 

 urchins and star-fishes. So called from the spines with 



which the integument is usually furnished. 

 Ec'tocyst (Gr. ektos, outside; kustis, a bladder). The outer 



covering of the Polyzoa. 

 Ec'toderm (Gr. ektos, outside; derma, skin). The outer layer 



of the body of an invertebrate animal, formed from the 



epiblast of the ovum. 

 Ectoproc'ta (Gr. ektos, outside ; proktos, the seat or anus). 



A group of Polyzoa in which the anus lies outside the 



circle of tentacles. 

 Ecto/te'rygoid (Gr. ektos, without; pteryx, a wing; eidos, 



shape). One of the bones of the skull in some Vertebrata. 

 Ec'tosarc (Gr. ektos, outside; sarx, flesh). The outer layer of 



sarcode in the Amoeba. 

 Edrioaste'rida (Gr. edraios, sitting, stable; aster, a star). A 



group of extinct Echinoderms. 

 Edriophthal'mia (Gr. edraios, sitting, stable; ophthalmos, an 



eye). A group of Crustaceans in which the eyes, when 



present, are either without stalks or seated upon immovable 



ones. 

 Efferent (L. e, out of; fero, I bear, carry). Carrying away, 



as the efferent nerves which carry nervous impulses from 



a nerve-centre. 

 Eges'ta (L. egestio, getting rid of). Material excreted by the 



alimentary canal. 

 Elasmobran'chii (Gr. elasmos, a plate; branchia, a gill). An 



order of fishes comprising the sharks, rays, and the chimaera. 

 Electro'tonos (Gr. elektron, amber; tonos, tension, tone). The 



electric condition of a nerve when a current of electricity 



passes through any part of it. 

 Ely'tra(Gr. elutron, a sheath). The front pair of chitinous wings, 



which in the beetles overlap the hinder membranous pair. 

 Em'boly (Gr. embole, injection). Another term for the 



invagination of the blastosphere in the development of 



the Invertebrata, whereby the hypoblast becomes enclosed 



within the epiblast. 

 Em'bryo (Gr. en, in; bruo, I swell). The earliest stage in 



which an animal may be discerned in the ovum. Also 



applied to the rudiment of the future plant in the seed. 



