688 



GLOSSARY 



tween the mammalian thoracic and 

 abdominal cavities. 

 Di-as'to-le ( Gr. dia, through; stellein, to set, 

 place). The relaxation phase of the 

 cardiac cycle. 

 Di-en-ceph'a-lon (Gr. dia, between; eng- 

 kephalon, brain ) . An area of the verte- 

 brate brain immediately posterior to 

 the cerebrum. 

 Dif'fer-en'ti-a"tion (L. diferre, to carry 

 apart). Specialization of cells and tis- 

 sues as a result of growth and develop- 

 ment. 

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

 movement of molecules as a conse- 

 quence of their kinetic energy. 

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

 conversion of food into materials that 

 can be absorbed and assimilated. 

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

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

 mixed offspring). The offspring of 

 parents differing in two characters. 

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



shape). Having two forms. 

 Di-oe'cious (diecious) (Gr. dis, twdce; 

 oikos, house ) . Having the sexes in sep- 

 arate individuals. 

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



tos, bud ) . Having two germ layers. 

 Diploid (Gr. diploos, double). The num- 

 ber of chromosomes in somatic cells. 

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



distant from the point of attachment. 

 Di-ur'nal (L. dies, day). Associated with 



daylight. 

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

 turn). A pouch or pocket leading out 

 from a tube. 

 Dor'sal (L. dorsum, back). The upper sur- 

 face of any animal. 

 Duct (L. ducere, to lead). A tube for the 



passage of metabolic products. 

 Duct'less gland. A gland which pours its 

 secretion directly into the blood 

 stream. 

 Du'o-de"num (L. diiodeni, 12 each). The 

 first part of the small intestine posterior 



to the stomach (about as long as the 



width of 12 fingers). 

 Du'ra ma'ter ( L. dura, hard; mater, 



mother). The tough outer covering of 



the brain and nerve cord. 

 Dys-gen'ic (Gr. dijs, hard, ill; gignesthai, 



to be born). Tending to bring about 



genetic degradation of a species. 



Ec-cen'tric (L. ex, without; centrum, cen- 

 ter). Away from center. 



Ee'dy-sis (Gr. ek, out; dijein, to enter). To 

 shed the exoskeleton, as in arthro- 

 pods. 



E-coro-gy (Gr. oikos, house; logos, dis- 

 course). The division of biology deal- 

 ing with the relation of plants and ani- 

 mals to their environment. 



Ec'to-derm (Gr. ektos, outside; derma, 

 skin ) . The outermost germ layer of the 

 gastrula which gives rise to the nervous 

 system. 



Ec'to-par"a-site (Gr. ektos, outside; para, 

 beside; sitos, food). A parasite which 

 lives on the outermost surface of its 

 host. 



Ec'to-plasm (Gr. ektos, outside; plasma, 

 something molded ) . The outer layer of 

 cytoplasm in a cell. 



Ec'to-sarc (Gr. ektos, outside; sarx, flesh). 

 The outer layer of certain Protozoa. 



Ef-fect'or (L. effectus, to effect). A nerve 

 end organ which serves to distribute 

 impulses which activate muscle con- 

 traction and gland secretion. 



Ef-f er'ent ( L. efferre, to bear out ) . Convey- 

 ing away from, as motor nerves that 

 conduct impulses away from the cord. 

 Egg (L. ovum, egg). The animal gamete or 



ovum formed by the female. 

 E-lec'tro-lyte (Gr. electron, amber; lijtos, 

 dissolved, dissoluble). A substance 

 which, when in solution, dissociates 

 into ions and thus conducts an electric 

 current. 

 El-ec'tron. The part of an atom having a 

 negative charge. 



