Appendix 827 



Determiner, see Gene. 



Dialysis (di-al'asis) (Gr. di, two; lysis, separating), separation of dissolved ma- 

 terials such as crystalloids from colloids by passage of former through a 

 semipermeable membrane; diffusion of certain substances in solution 

 through a membrane but not of other substances. 



Diaphragm (di'afram) (Gr. diaphragma, partition), muscle separating thoracic 

 and abdominal cavities. 



Diastase (di'astas) (Gr. dia, through; histanai, to set), enzyme which converts 

 starch into sugar. 



Dichotomous (di -kot' o mus) (Gr. dicho, two; tome, divide), repeated forking 

 into two parts. 



Dieclous (di-e'shus) (Gr. di, two; oikos, house), having male and female sex 

 organs in separate individuals (contrast with Monecious). 



Differentiation (specialization), process of becoming structurally or functionally 

 unlike the original condition. 



Diffraction (di -frak' shun) (L. diffractus, break), deflection of light waves when 

 passing through a narrow slit to form fringes of parallel light and dark- 

 colored bands. 



Diffusion (di -fu' zhun) (L. diffusia, spread), passage of molecules of one sub- 

 stance among those of another from a region of greater concentration to 

 one of less concentration. 



Digestion (di -jes' chun) (L. digestio, dissolve food), preparing food for absorp- 

 tion. 



Dihybridization (di hy brid i -za' shun) (Gr. di, two; hyhrida, mongrel), produc- 

 ing an offspring from parents who differ with regard to two given char- 

 acters. 



Dimorphism (di -mor' fizm) (Gr. di, two; morphe, form), two forms or types 

 belonging to one species, as males and females of same species but differing 

 from each other. 



Diphyletic tree (dif i -let' ik) (Gr. diphy, twofold), schematic, treelike representa- 

 tion of the supposed ancestral relations of various animals and plants. 



Diploblastic (dip lo -bias' tik) (Gr. diplos, two; blast os, germ), two germ layers 

 (ectoderm and entoderm). 



Diploid (dip' loid) (Gr. diplos, two), double number of chromosomes found in 

 the sporophyte generation of plants and body cells of animals as contrasted 

 with single number in germ cells (contrast with Haploid). 



Diplopoda (dip -lop' o da) (Gr. diploos, double; pous, foot), millipedes. 



Diptera (dip' tura) (Gr. di, two; ptera, wings), insects with the two wings (one 

 pair) as flies, mosquitoes, gnats, etc. 



Direct cell division, see Amitosis. 



Discontinuous distribution, two species occurring in two or more widely sepa- 

 rated regions, suggesting that their distributions may at one time have 

 been continuous. Tapirs exist only in Malay and tropical America. 



Discontinuous variation, see Mutation. 



Distal (dis' tal) (L. dis, apart; stare, to stand), farthest from median line. 



Divergence (adaptive radiation), somewhat closely related species radiate in vari- 

 ous directions into different environments and become modified (vary) 

 accordingly. 



