GLOSSARY. 58l 



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



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



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



the feet. 

 DIMEROSOMATA (Gr. dis ; meros, part; soma, body). An order of Arachnida, 



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. 

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



to species which consist of male and female individuals. 

 DIPHYOZOOIDS. Detached reproductive portions of adult Calycophoridcc, an 



order of oceanic Hydrozoa, 

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



those Mammals which have two sets of teeth. 

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



the Lepidosircn. 

 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 Medusae, 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. diver ticulum, a bye-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. dorsnm, the back ; Gr. Iragckia, gill). Having ex- 

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



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



employed. 



ECDERON (Gr. eJc, out ; deros, 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. 



ECHINOCOCCI (Gr. echinos, a hedgehog ; kokkos, a berry). The larval forms 

 (scolices) of the tapeworm of the dog (Ttznia 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. 



ECHIXOIDEA (Gr. echinos ; and eidos, form). An order of Mchinodermata, com- 

 prising the Sea-urchins. 



ECHINULATE. Possessing spines. 



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

 the ccenoecium of a Polyzoon. 



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

 the Ccelenterata. 



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

 tain Rhizopods, such as the A mceba. 



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

 called Unita. 



