GLOSSARY OF TECHNICAL TERMS xvii 



BIOGENESIS (Gr. jftt'os, life; yeWo-ts, birth), the origin' of living 



things from pre-existing living things. 

 BIOGENETIC LAW (Gr. (Bios, life ; yeWcns, origin), Haeckel's term for 



the recapitulation hypothesis. 

 BIOLOGY (Gr. /3to?, life ; Ao'yoy, discourse), the science of living 



things. 

 BIOPHORS (Gr. i'oj, life; cfyopevs, carrier), the smallest living 



units of which protoplasm is composed (according to Weis- 



mann's theory). 

 BLASTOCCEL (Gr. /3Aaoros, embryo ; KotAoi>, a hollow), the cavity 



of a blastula embryo. 

 BLASTODERM (Gr. /3Aaoroj, embryo ; ^p^a, skin), a layer of cells 



which in heavily yolked eggs spreads over the surface and 



gives rise to the embryo. 

 BLASTOGENIC (Gr. /SAaoro'j, germ ; rt. yer-, origin), a term 



applied to characters which originate in the germ cells. 

 BLASTOMERES (Gr. /3Aaoro's, embryo; /xepos, part), the undif- 



ferentiated cells into which a developing egg first divides. 

 BLASTOPORE (Gr. /SAaoros, embryo ; WO/DOS, passage), the mouth 



of a gastrula embryo. 

 BLASTOSPHERE (Gr. jSAaoros, embryo ; o-^cupa, sphere), a hollow, 



spherical embryo composed of a single layer of cells. 

 BLASTOSTYLES (Gr. BAaoros, embryo ; crruAo?, pillar), the rod- 

 shaped individuals which in certain hydroid colonies (e.g., 



Obelia) bear the developing medusae. 

 BLASTULA, another name for blastosphere (q.v.). 

 BRACHIOPODS (Gr. 8payj><*>v, arm ; TTOVS, foot), invertebrate animals 



which bear a superficial resemblance to bivalve Mollusca, 



but belong to a totally different group, known as Brachio- 



poda ; sometimes called lamp shells. 

 C^ENOGENETIC (Gr. Kdivos, recent ; yeVecris, origin), a term applied 



to characters of comparatively recent origin. 

 CAINOZOIC (Gr. KCLIVOS, recent ; 0077, life), a term applied to the 



most recent of the main divisions of the earth's history, 



during which the more modern forms of living things 



appeared. 

 CALYX (Gr. KaAuf, calyx), the outermost of the whorls of modified 



leaves of which a typical flower is composed. 

 CAMBIUM (late Lat., exchange), a layer of cells which lies between 



the wood and the bast and which, by cell division, causes 



increase in the thickness of both. 



B. b 



