GLOSSARY. 569 



outer layer of the body amongst the Infusoria. The outer layer of the 



integument generally. 

 CYCLOID (Gr. kuklos, a circle ; eidos, form). Applied to those scales of fishes 



which have a regularly circular or elliptical outline with an even margin. 

 CYCLOSTOMI (Gr. kuklos, and stoma, mouth). Sometimes used to designate 



the Hag-fishes and Lampreys, forming the order Marsipobranchii. 

 CYST (Gr. kustis, a bladder or bag). A sac or vesicle. 

 UYSTOIDEA (Gr. kustis, a bladder; and eidos, form). An extinct order of 



Echinodermata. 



DECAPODA (Gr. deka, ten ; podes, 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. decido, I fall off). Applied to parts which fall off or are 



shed during the life of the animal. 

 DECOLLATED (Lat. decollo, I behead). Applied to univalve shells, the apex of 



which falls off in the course of growth. 



DEINOSAURIA (Gr. deinos, terrible ; saura, lizard). An extinct order of Rep- 

 tiles. 

 DENDRIFORM, DENDRITIC, DENDROID (Gr. dendron, a tree). Branched like a 



tree, arborescent. 



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

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



epidermis. 



DEXTRAL (Lat. dextra, the right hand). Right-handed. Applied to the di- 

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

 DIAPHRAGM (Gr. diaphragma, a partition). The "midriff" or the muscle 



which in Mammalia forms a partition between the cavities of the thorax 



and abdomen. 

 DIASTEMA (Gr. dia, apart ; histemi, to place). A gap or interval, especially 



between teeth. 

 DIATOMACE.E (Gr. diatemno, 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. 

 DICYNODONTIA (Gr. dis, twice; kuon, dog; odovs, tooth). An extinct order 



of Reptiles. 

 DIDELPHIA (Gr. dis, twice ; delphus, womb). The subdivision of Mammals 



comprising the Marsupials. 

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



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

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



the feet. 

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



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

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



those Mammals which have two sets of teeth. 

 DIPNOI (Gr. dis, twice ; piwe, 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 desig- 

 nate 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- 



