662 GLOSSARY. 



DIGIT (Lat. digitus, a finger). A finger or toe. 



DIGITIGRADA (Lat. digitus ; gradior, I walk). A subdivision of the Carnivora. 



DIGITIGRADE. Walking upon the tips of the toes, and not upon the soles of 



the feet. 

 DIMEKOSOMATA (Gr. dis ; meros, part ; soma, body). An order oiArachnida, 



comprising the true Spiders, so called from the marked division of the body 



into two regions, the cephalothorax and abdomen. The name Araneida is 



often employed for the order. 

 DIMYARY (Gr. dis, twice ; muon, muscle). Applied to those bivalve Molluscs 



(Lamellibranchiata) in which the shell is closed by two adductor muscles. 

 DHECIOUS (Gr. dis, twice ; oikos, house). Having the sexes distinct ; applied 



to species which consist of male and female individuals. 

 DIPHYODONT (Gr. dis, twice ; phuo, I generate ; odous, tooth). Applied to 



those Mammals which have two sets of teeth. 

 DIPHYOZOOIDS. Detached reproductive portions of adult Calycophoridce, an 



order of oceanic Hydrozoa. 

 DIPNOI (Gr. dis, twice ; pnoe, breath). The order of fishes represented by 



the Lepidosiren. 

 DIPTERA (Gr. dis, twice ; pteron, wing). An order of Insects characterised 



by the possession of two wings. 



DISCOID (Gr. diskos, a quoit ; eidos, form). Shaped like a round plate or quoit. 

 DISCOPHORA (Gr. diskos, a quoit ; phero, I carry). This term is applied to 



the Medusce, or Jelly-fishes, from their form; and is sometimes used to 



designate the order of the Leeches (Hirudinea) from the suctorial discs 



which these animals possess. 

 DISSEPIMENTS (Lat. dissepio, I partition off). Partitions. Used in a restricted 



sense to designate certain imperfect transverse partitions, which grow from 



the septa of many corals. 

 DISTAL. Applied to the quickly growing end of the hydrosoma of a Hydro- 



zoon ; the opposite, or "proximal," extremity growing less rapidly, and 



being the end by which the organism is fixed, when attached at all. 

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



day. 

 DIVERTICULUM (Lat. diverticulum, a by-road). A lateral tube with a blind 



extremity springing from the side of another tube. 

 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 A nnelides and Molluscs. 



The term is of mongrel composition, and "notobranchiate" is more correctly 



employed. 



ECDERON (Gr. ek, out ; deros, skin). The oiiter 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. 



ECHINOCOCCI (Gr. echinos, a hedgehog ; 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 ccencecium of a Polyzoon. 



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

 of the Cozlenterata. 



ECTOSARC (Gr. ektos ; sarx, flesh). The outer transparent sarcode-layer of 

 certain Rhizopods, such as the Amoeba. 



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

 called Bruta. 



