GLOSSARY 



669 



sperm produced by another individual. Op- 

 posite of self-fertilization. 



Cross'ing o'ver. The process in which homo- 

 logous chromosomes break and exchange 

 corresponding segments. 



Cu-ta'ne-ous ( L. cutis, skin ) . Pertaining to the 

 skin. 



Cu'ti-cle (L. cutis, skin). A thm, noncellular, 

 outermost covering of an organism. 



Cy-clo'sis (Gr. kyklosis, whirling round). The 

 rotar)' streaming movement of the proto- 

 plasm in certain cells. 



Cyst (Gr. kystis, a bladder). An organism en- 

 closed in a thickened resistant wall; a sac 

 or bladdcrlike structure. 



Cy-toro-gy (Gr. kytos, hollow; logos, dis- 

 course). The science which deals with the 

 structure of cells. 



Cy'to-phar"ynx (Gr. kytos, hollow; pharynx, 

 gullet) . The pharynx or gullet of a protozoan 

 such as Paramecium. 



Cy'to-plasm (Gr. kytos, hollow; plasma, some- 

 thing molded). The protoplasm of a cell 

 exclusive of the nucleus. 



Dac'tyl (Gr. daktylos, finger). Referring to the 

 finger or toe. 



Dar'win-ism. Darwin's theory that species have 

 originated by natural selection. 



Daugh'ter cells. The two cells that have been 

 formed by the division of one cell. 



Def-e-ca'tion (L. de, from; faecis, dregs). The 

 passage of waste material from the digestive 

 tract of an animal. 



Den'drite (Gr. dendron, tree). A fiber of a 

 nerve cell that conducts impulses toward 

 tlic nerve cell body. 



Den'ta-ry (L. dens, tooth). The upper bone 

 of the lower jaw of a vertebrate. 



Der'mal (Gr. derma, skin). Pertaining to the 

 skin, especially the inner connective tissue 

 layers of the vertebrate skin. 



Der'mis (Gr. derma, skin). The inner layer 

 of the skin, lying below the epidermis. The 

 term is synonymous with corium. 



Di-al'y-sis (L. dialysis, separation). The separa- 

 tion of crvstalloids and colloids in solution 

 by means of their unequal diffusion through 

 certain natural or artificial membranes. 



lyi'a-phragm (Gr. diaphragma, iniunfrj. A 

 sheetlike muscle forming a partition between 

 the thoracic and abdominal cavities in mam- 

 mals. A dividing membrane. 



Di-cji-ceph'a-lon (Gr. dia, between; engkepha- 

 lon, brain). A region of the vertebrate brain 

 just posterior to the cerebrum in the adult. 

 In the embryo, the second of two divisions 

 of the prosencephalon. 



Dif'fer-en'ti-a"tion (L. differre, to carry apart). 

 The process whereby cells and tissues be- 

 come specialized for specific functions dur- 

 ing the process of dexelopnicnt and growth. 



Dif-fu'sion (L. diffundere, to pour). The 

 movement of molecules from a region of 

 high concentration to one of lower concen- 

 tration brought about as a consequence of 

 their kinetic energy. 



Di-ges'tion (L. digestio, digestion). The con- 

 version of complex, unabsorbable food mate- 

 rial into soluble forms that may be absorbed. 



Dig'it (L. digitus, finger). A finger or toe. 



Dig"i-ti-grade' (L. digitus, finger, toe; gradi, to 

 walk). Walking on the toes. 



Di-hy'brid (Gr. dis, twice; L. hibrida, mixed 

 offspring). The progeny or offspring of par- 

 ents that differ in 2 traits (characters); an 

 individual which is hybrid (heterozvgous) 

 with respect to 2 pairs of genes. 



Di-mor'phism (Gr. dis, twice; morphe, shape). 

 Difference in size, structure, form, color, 

 etc., between 2 types of individuals of the 

 same species. 



Di-oe'cious (Gr. dis, twice; oikos, house). Hav- 

 ing the male and female reproductive organs 

 in separate individuals. 



Dip'lo-blas'tic (Gr. diploos, double; blastos, 

 bud ) . Dcri\cd from 2 embryonic germ lavers, 

 ectoderm and endoderm. 



Dip'loid (Gr. diploos, double). Referring to 

 the number of chromosomes in somatic cells; 

 double the number of chromosomes that oc- 

 cur in the mature egg or sperm. 



Dis-sim'i-la"tion. The disintegration of proto- 

 plasm principally by oxidation. 



Dis'tal (L. dis, apart; stare, to stand). Away 

 from the point of attachment; for example, 

 the hand is the distal part of the arm. Op- 

 posite of proximal. 



Di-ur'nal (L. dies, day). Pertaining to the time 

 of daylight. It is opposed to nocturnal, which 

 pertains to the time of night. 



Di'ver-tic'u-lum ( L. de, away; vertere, to turn ) . 

 A saclike projection of a tubular organ. 



Dom'i-nant trait ( char'ac-ter ) (L. dominus. 

 master). A trait which appears as the result 

 of either a single or a double "dose" of a 



