378 PRINCIPLES OF ANIMAL BIOLOGY 



Deficiency disease. Any disease resulting from the lack or scarcity of some specific 



substance in the diet. 

 Democritus {de mok' ri tus). Greek philosopher, known for his atomic theory, who 



lived about 460-357 b.c. 

 Demospongiae {de' mo spun' ji ee). A class of Porifera (sponges). For definition see 



Chap. 19. 

 Dendrite. A projection from a nerve cell which ordinarily conducts impulses toward 



the body of the cell. 

 Dendritic. Treehke. 

 Denticulate. Finely notched or toothed. 



Dentine. The dense bony substance composing the bulk of mammalian teeth. 

 Dermatozoa {der' ma to zo' a). A group of animals (literally, the skin or touch 



animals) in Oken's early classification. It comprised the invertebrates. 

 Dero. A genus of worms, phylum Annelida, subclass Oligochaeta. 

 Determinate. Leading infallibly to a given end result from a given beginning; said 



of development in which each cleavage cell produces a certain structure and 



nothing else, regardless of experimental interference. 

 Devonian (de vo' ni an). Of middle Paleozoic age, next following the Silurian. 

 Dextrin. Any one of several related carbohydrates derived by hydrolysis from starch, 



among them being erythodextrin, achroodextrin, and maltodextrin. 

 Diaphragm {di' afram). A partition; specifically, the partition between the thorax 



and abdomen of a mammal. 

 Diffusion. The spreading of the molecules of one substance among those of another. 

 Digestion. The conversion of food into soluble substances which may diffuse through 



protoplasm. 

 Dinosaur {di' no sawr). One of an order of extinct reptiles of Mesozoic time, mostly 



of large size. 

 Dinotherium {di' no the' ri um). An extinct elephantlike animal from the Miocene. 

 Dioecious {di ee' shus). Having the male and female organs in separate individuals; 



said of species. 

 Diogenes {di oj' e neez). Greek natural philosopher of the fifth century before Christ, 



born at ApoUonia. 

 Diploblastic. Composed of two layers of cells. 

 Diploid {dip' laid). Double; specifically, the double number of chromosomes found 



in the somatic cells, and in germ cells before meiosis, in bisexual animals. Cf. 



haploid. 

 Dipnoi {dip' no i). A subclass of Pisces, fishes with an air bladder functioning as a 



lung; the lungfishes. 

 Disaccharide {di sak' a ride). A carbohydrate whose molecule can be split into two 



molecules of simple sugar (monosaccharide). 

 Dominant. Receiving expression when only one determining gene is present, and 



in the presence of the gene for a contrasted recessive character; said of inherited 



characters that are exhibited by heterozygotes. 

 Dorsal. Pertaining to the back; hence, usually, upper. 

 Dorsal aorta. A large artery formed, in fishes, by the union of vessels coming from 



the gills, and passing backward in the dorsal region. 

 Dorsal root. The dorsal one of two roots by which a spinal nerve is connected with 



the spinal cord. Its fibers are sensory in function. 

 Drosophila {dro sof i la). A genus of flies, of which the vinegar fly (D. melanogaster, 



met' a no gas' ter) is a common species. 

 Duodenum {du' o de' num). The first of three divisions of the small intestine. 

 Dutrochet, Rene Joachim Henri {dii' tro' shay'). French physiologist, 1776-1847. 



