330 GLOSSARY. 



DEX'TRAL (Lat. dextra, the right hand). Eight-handed : applied to the direc- 

 tion of the spiral in the greater number ol univalve shells. 



DI'A-PHRAGM (Gr. diaphragma, a partition). The "midriff," or the muscle 

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

 and abdomen. 



DI-A-STE'MA (Gr. dia, apart; Tiistemi, to place). A gap or interval, especially 

 between teeth. 



DI-AS'TO-LE (Gr. diastello, I separate or expand). The expansion of a contrac- 

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



DI-A-TO-MA'CE-JE (Gr. diatemno, I sever). An order of minute plants, which 

 are provided with siliceous envelopes. 



DI-BRAXCH-I-A'TA (Gr. dis, twice; bragchia. gills). The order of Cephalopoda, 

 (comprising the Cuttle-fishes, etc.), in winch only two gills are present. 



DI-OYK-O-DON'TI-A (Gr. dis, twice ; kuon, dog ; odous, tooth). An extinct order 

 of Keptiles. 



DI-DEL'PHI-A (Gr. dis, twice ; delphus, womb). The subdivision of Mammals 

 comprising the Marsupials. 



DIG'IT (Lat. digitus, a finger). A finger or toe. 



DIG-I-TI-GRA'DA (Lat. digitus; gradior, I walk). A subdivision of the Car- 

 nivora, 



DIG'I-TI GRADE. Walking upon the tips of the toes, and not upon the soles 

 of the feet. 



DIM-E-RO-SO'MA-TA (Gr. dis ; meros, part; soma, body). A.n 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. 



DIM'Y-A-RY ( Gr. du, twice ; mus, muscle). Applied to those bivalve Molluscs 

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



DI-CE'OIOUS (Gr. dis, twice ; oikos. house). Having the sexes distinct; applied 

 to species which consist of male and female individuals. 



DIPH'Y-O-DONT (Gr. dis. twice; phuo, I generate; odous, tooth). Applied to 

 those Mammals which have two sets of teeth. 



DIPH-Y-O-ZO'OIDS. Detached reproductive portions of adult Calycophorida, an 

 order of oceanic Hydroaoa. 



DIP'NOI (Gr. dis, twice; pnoe, breath). The order of Fishes represented by 

 the Lepidosiren. 



DIP'TER-A (Gr. dis, twice ; pteron, wing). An order of Insects characterized 

 by the possession of two wings. 



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



DIS-COPH'O-RA (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. 



DIS-SEP'I-MENTS (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. 



DIS'TAL. 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. 



DI-UR'NAL (Lat. dies, day;. Applied to animals which are active during the 

 day. 



DI-VER-TIO'U-LUM (Lat. diverticulum, a by-road). A lateral tube with a blind 

 extremity springing from the side of another tube. 



DOR'SAL (Lat. dorsum, back). Connected with the back. 



DOR-SI-BRANCH'I-ATE (Lat. dorsum, the back ; Gr. bragckia, gills). Having ex- 

 ternal gills attached to the back ; applied to certain Annetides and Molluscs. 

 The term is of mongrel composition, and " notobranchiate " is more cor- 

 rectly employed. 



EO'DE-ROH (Gr. ek, out: deros, skin). The outer plane of growth of the ex- 

 ternal integumentary layer (.viz., the ectoderm, or epidermis). 



