ARA- 



21 



ARC- 



tissue consisting of thin -walled 

 watery parenchymatous cells (bot.}. 



arachnid (arak'md) a. [Gk. arachne, 

 spider.] Spider-like, pert, spiders 

 (goo/.). 



arachnidium (araknid'ium) n. [Gk. 

 arachne, spider.] The spinning 

 apparatus of a spider, including 

 spinning-glands and spinnerets 

 (sool.}. 



arachnoid (arak'noid) a. [Gk. arach- 

 ne, spider ; eidos, form.] Like a 

 cobweb ; consisting of fine en- 

 tangled hairs resembling a cobweb 

 (bot.} ; appl. a thin membrane of 

 the central nervous system, com- 

 posed of delicate connective tissue 

 with an endothelial covering on its 

 free surfaces and lying between the 

 dura and the pia mater (ana/.} ; 

 pert, or resembling a spider (zool.}. 



arborescent (ar'bore's'e'nt) a. [L. ar- 

 borescens, growing like a tree.] 

 Branched like a tree (bot.}. 



arboroid (ar'boroid) a. [L. arbor, 

 tree ; Gk. eidos, like.] Tree-like, 

 designating general structure of a 

 protozoan colony (zool.}. 



arbor vitae (ar'bor vl'te, ve'ta) n. [L. 

 arbor, tree ; -vita, life.] The tree 

 of life, appl. arborescent appear- 



- ance of the cerebellum in vertical 

 . section (anat.}. 



arbutean (arbu'tean) a. [L. arbutus, 

 strawberry tree.] Of or pert, the 

 strawberry tree (bot.}. 



arcade (arkad') n. [L. arcus, a bow.] 

 An arched channel or passage ; a 

 bony arch, as supra- and infra- 

 temporal arches in the skull (anat.}. 



archaeocytes (ar'keoslts) n.plu. [Gk. 

 archaios, ancient ; kytos, hollow.] 

 Cells arising from undifferentiated 

 blastomeres and ultimately giving 

 rise to germ-cells and gametes 

 (emb.}. 



archaeostomatous (ar'keosto'm'atus) a. 

 [Gk. archaios, primitive ; stoma, 

 mouth.] Having the blastopore per- 

 sistent and form ing the mouth (zool.}. 



arch-centra (ark'-seVtra) n. plu. [Gk. 

 archi, beginning, first ; L. centrum, 

 centre.] Centra formed by fusion 

 of basal growths of primary arcualia 

 external to chordal sheath ; cf. 

 chordacentra (zool.}. 



archebiosis (ar'keblo'sls) n. [Gk. 



arche, beginning ; bios, life.] The 

 origin of life (biol.}. 



archegoniophore (ar'kego'niofor) n. 

 [Gk. arche, beginning ; gonos, off- 

 spring ; pkerein, to bear.] Branches 

 of mosses bearing archegonia (bot.}. 



archegonium (ar'kego'mum) n. [Gk. 

 arche, beginning ; gonos, offspring.] 

 A female organ in which the 

 oospheres are formed, and in which 

 the young plant begins its develop- 

 ment (bot.}. 



archenteron (arkgn'tgron) n. [Gk. 

 arche, beginning ; enteron, gut.] 

 The cavity of the gastrula which 

 forms the primitive gut of the 

 embryo (emb.}. 



archespore (ar'kespor) n. [Gk. arche, 

 beginning ; sporos, seed.] The 

 tetrahedral or meristematic cell of 

 a sporangium (bot.}. 



archiamphiaster (ar'kTam'fTas'te'r) n. 

 [Gk. archi, first ; amphi, on both 

 sides ; aster, star.] The amphiaster 

 forming the first or second polar 

 body in cell maturation (cyt.}. 



archiblast (ar'kiblast) n. [Gk. archi, 

 first ; blastos, bud.] Egg proto- 

 plasm. 



archiblastic (ar'kiblas'tik) a. [Gk. 

 archi, first ; blastos, bud.] Having 

 total and equal segmentation (cyt.}. 



archiblastula (ar'kiblas'tula) n. [Gk. 

 archi, first ; blastos, bud.] Typical 

 hollow ball of cells derived from an 

 egg with total and equal segmenta- 

 tion (cyt.}. 



archicarp (ar'kikarp) n. [Gk. archi, 

 first ; karpos, fruit.] The spirally 

 coiled region of the thallus of 

 certain fungi (bot.}. 



archicerebrum (ar'kise'r'e'brum) n. 

 [Gk. archi, first ; L. cerebrum, brain.] 

 The primitive brain, as the supra- 

 oesophageal ganglia of higher 

 Invertebrates (zool.}. 



archichlamydeous (ir'kiklamid'eus) a. 

 [Gk. archi, first ; chlamys, cloak.] 

 Having no petals, or having petals 

 entirely separate from one another 

 (bot.}. 



archicoel (i/kisel) n. [Gk. archi, 

 first ; koilos, hollow.] The primary 

 body- cavity or space between v the 

 alimentary canal and ectoderm in 

 development of various groups of 

 animals (zoo/.}. 



