GLOSSARY. 25 



CYSTOIDEA (Gr. Jcustis, a bladder ; and eidos, form). An extinct order of 

 Echinodermata. 



DECAPODA (Gr. deka, ten, poda, feet). The division of Crustacea, which 



have ten ambulatory feet; also the family of Cuttle-fishes, in which there 



are ten arms or cephalic processes. 

 DECIDUOUS (Lat. dtcido, I fall off). Applied to parts which fall off or are 



shed during the life of the animal. 

 DECOLLATED (Lat. d(collo, I behead). Applied to univalve shells, the apex 



of which falls off in the course of growth. 

 DENDEIFOBM, DENDEITIC, DENDEOID (Gr. dendron, a tree). Branched like 



a tree, arborescent. 



DERMAL (Gr. derma, skin). Belonging to the integument. 

 DERMOSCLERITES (Gr. derma, skin, skltros, hard). Masses of spicules which 



occur in the tissues of some of the Alcyonidce (Actiitozoa). 

 DESMIDI^E. Minute fresh-water plants, of a green colour, without a siliceous 



epidermis. 

 DEUTEROZOOIDS (Gr. deuteros, second; zobn, animal; eidos, form). The 



zoo'ids which are produced by gemmation from zooids. 

 DEXTRAL (Lat. dextra, the right hand). Eight-handed ; applied to the di- 

 rection of the spiral in the greater number of univalve shells. 

 DIASTOLE (Gr. diastcllo, I separate or expand). The expansion of a contractile 



cavity such as the heart, which follows its contraction or ' systole.' 

 DIATOMACE^B (Gr. diatcmno, I sever). An order of minute plants, which are 



provided with siliceous envelopes. 

 DIBRANCHIATA (Gr. dis, twice ; bragchia, gill). The order of Cephalopoda 



(comprising the Cuttle-fishes, &c.) in which only two gills are present. 

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



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

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



to species which consist of male and female individuals. 

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



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



body into two regions, the cephalothorax and abdomen. The name Ara- 



neida is often employed for the order. 

 DIPHYOZOOIDS. Detached reproductive portions of adult Calycophoridce, an 



order of oceanic Hydrozoa. 

 DIPTERA (Gr. dis, twice ; pttron, 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. 

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



the Medusa, 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 re- 

 stricted 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. 

 DIVEETICULUM (Lat. diverticulum, a bye-road). A lateral tube with a blind 



extremity, springing from the side of another tube. 

 DOESIBBANCHIATE (Lat. dorsum, the back; Gr. bragchia, gill). Having 



external gills attached to the back; applied to certain Annelides and 



