GLOSSARY 



665 



kylindein, to roll). The rodlike central por- 

 tion of a mcdullated nerve fiber. 



Ax'o-lotl (Sp. axolotl, ser\ant of water). A 

 pedogenic larvae of any of several species 

 of salamander of the genus Ambystoma 

 found in Mexico and the southwestern part 

 of the United States. Originally applied to 

 a Mexican species only; now, by extension, 

 to others. 



Ax'on (Gr. axon, axle). The fiber of a nerve 

 cell that conducts impulses away from the 

 cell bodv of which it is a part. 



Az'y-gos (Gr. a, without; zygon, yoke). An 

 unpaired anatomic structure such as the 

 azygos vein of mammals. 



Back'bone. The \ertebral column, especially 

 if composed of bone. 



Back'cross. The mating of a hybrid to either 

 of its parents. 



Bar'ri-er (F. bane, bar). Any type of obstruc- 

 tion — physical, chemical, or biological — 

 that prevents the migration of animals, or 

 gradual extension of their territories. 



Be-hav'ior. The reactions of the whole organ- 

 ism to its environment. 



Ben'e-dict's so-lu'tion (After Benedict. L. 

 solutio, from solvere, to dissohe ) . An alka- 

 line copper sulfate solution, blue in color. 

 If a few drops of a reducing sugar solution 

 are added after heating the copper solution, 

 the cupric copper is reduced to the cuprous 

 state, and a change to a reddish color is 

 noted. Used as a test for the presence of 

 sugars in solution. 



Ben'thos (Gr. benthos, depth of the sea). 

 Those organisms living on or in the bottom, 

 cither of the ocean or fresh waters, from the 

 edge of water down to the greatest depths. 



Bi-lat'er-al sym'me-try (L. bis, twice; latus, side. 

 Gr. syn, with; metron, measure). The ar- 

 rangement of the parts of an organism in 

 such a way that the right and left hahes of 

 the body are mirror images of each otncr. 



Bile (L. bills, bile). A fluid which is secreted 

 by the liver in vertebrates. 



Bile duct (L. ducere, to lead). The duct which 

 transports bile from the gall bladder to the 

 small intestine. 



Bi'na-ry fis'sion (L. bis, twice. L. fissus, cleft). 

 That t\'pe of asexual reproduction by means 



of which an organism divides into two ap- 

 proximately equal parts. 



Bi-no'mi-al (L. bis, twice; nomen, name). 

 Having two names; in nomenclature the first 

 is known as the generic and the second as 

 the specific name. 



Bi-o-gen'e-sis (Gr. bios, life; genesis, birth). 

 The doctrine that living things are produced 

 only from living things — the opposite of 

 abiogenesis. 



Bi'o-ge-nef'ic law (Gr. bios, life; genesis, pro- 

 duction). The principle that an animal may 

 repeat in its embryonic development some of 

 the corresponding stages of its ancestors; 

 also known as the recapitulation theory. 



Bi-oro-gy (Gr. bios, life; logos, discourse). 

 The science of life; it includes botanv, 

 zoologv, and all the fields of studv associated 

 with life. 



Bi'o-lu'nii-nes"cence (Gr. bios, life; L. lumen, 

 light). The production of light as the result 

 of chemical reactions in living organisms. 



Bi-ra'di-al sym'metry (L. bis, having two; 

 radius, ray). The condition in which an 

 animal has radially arranged parts that lie 

 half on one side and half on the other side 

 of a median longitudinal plane; example, the 

 Ctenophora. 



Bi-ra'mous ap-pend'age (L. bis, ha\'ing two; 

 ramus, branch ) . A two-branched structure. 



Blast (Gr. blasteo, to sprout). A combining 

 form inferring formation or de\'elopment. 



Blas'to-coel (Gr. blastos, bud; koilos, hollow). 

 The cavity present within the blastula. 



Blas'to-mere (Gr. blastos, bud; meros, part). 

 A cleavage cell; any one of the cells in an 

 embryo from the first cleavage division to 

 the beginning of gastrulation. 



Blas'to-pore (Gr. blastos, bud; poros, passage). 

 The porclike opening from the archcnteron 

 or gastrula cavity to the exterior. 



Blas'tu-la ( Gr. blastos, bud ) . An early develop- 

 mental stage of an embryo, usually a hollow 

 ball of cells. 



Bow'man's cap'sule (After Sir Wm. Bowman, 

 English physician. L. capsula, little box). 

 The cup-shaped end of a kidney tubule that 

 forms around a glomerulus. 



Bra'chi-al (L. brachium, arm). Belonging or 

 pertaining to the upper part of the forelinib 

 of a vertebrate. 



Bran'chi-a (Gr. branchia, gills). Gills. 



