MED. 



179 



MEG- 



tween the pith and the pericycle 

 (**} 



medullary sheath, a ring of pro- 

 toxylems round the pith of certain 

 stems (dot.) ; a layer of white 

 glistening material surrounding 

 the axis cylinder of a medullated 

 nerve-fibre (zool.). 



medullated (mgdula'tSd) a. [L. 

 medulla, pith.] Provided with a 

 medullary sheath. 



medullated nerve-fibres, the fibres 

 of the white part of the brain and 

 spinal cord, consisting of an axis- 

 cylinder or neuraxis of primitive 

 fibrillae, surrounded by medullary 

 sheath, which is in turn covered by 

 a delicate membrane, the neuri- 

 lemma (anat.). 



medullispinal (mgdul'ispi'nal) a. [L. 

 medulla, pith ; spina, the spine.] 

 Of the spinal cord. 



medusa (mgdu'sa) n. [Gk. Medousa, 

 one who rules.] A jelly-fish (zool.). 



medusiform (medu'siform) a. [Gk. 

 Medousa, Medusa ; L. forma, 

 shape.] Like a medusa or jelly-fish. 



medusoid (medu'soid) n. [Gk. 

 Medousa, Medusa ; eidos, like.] 

 A medusa - like free - swimming 

 gonophore of Hydrozoa (zool.) ; a., 

 like a jelly-fish or medusa (zool.). 



medusome (mSdu'som) n. [Gk. 

 Medousa, Medusa ; soma, body.] 

 A name given to the medusoid 

 stage in the life-history of Obelia 

 (zool.). 



megagamete (mgg'agamet) n. [Gk. 

 megas, large ; gametes, a spouse.] 

 A rounded cell regarded as an 

 ovum or its equivalent ; developed 

 from a megagametocyte after a 

 process akin to maturation (zool.). 



megagametocyte (mgg'agame'toslt) 

 n. [Gk. megas, large ; gametes, a 

 spouse ; kytos, hollow.] A cell 

 developed from a merozoite, and 

 itself giving rise to a megagamete, 

 frequently requiring transference 

 to another host before its develop- 

 ment can proceed (zool.). 



megakaryocyte (meg'akar'ioslt) n. 

 [Gk. megas, large ; karyon, nut ; 

 kytos, hollow.] A giant-cell of 

 marrow with one large annular 

 lobulated nucleus, containing a 

 number of nucleoli (anat.). 



megalaesthetes (meYaleVthets) . 

 plu. [Gk. megalon, great ; aistheti- 

 kos, perceptive.] Sensory organs, 

 sometimes in the form of eyes in 

 the Placophora (zool.). 



megaloblast (meg'aloblast) n. [Gk. 

 megalon, great ; blastos, bud.J A 

 large erythroblast (anat.). 



megalogonidlum (mgg'alogonTd'Ium) 

 n. [Gk. megalon, great ; gonos, 

 offspring.] A large gonidium (dot.). 



megalopa (mfig'alo'pa). Megalops. 



megaloplc (mgg'alop'ik) a. [Gk. 

 megalon, great ; ops, eye.] Be- 

 longing to the megalops stage 

 (zool.). 



megalopore (meg'alopor) n. [Gk. 

 megalon, great ; poros, a channel.] 

 A pore in the dorsal plates in 

 Chiton for placing a megalaesthete 

 in direct communication with the 

 exterior (zool.). 



megalops (me'g'alops) n. [ Gk meg- 

 alon, great ; os, eye.] A larval 

 stage of certain Crustaceans, as 

 crabs, conspicuous by large stalked 

 eyes (zool.). 



megalospherlc (mgg'alosfgr'ik) a. 

 [Gk. megalon, great ; sphaira, a 

 globe.] Of polythalamous Foramin- 

 ifer shells, having a megalosphere 

 or large initial chamber (zool.}. 



megamere (meg'amer) n. [Gk. megas, 

 large ; meros, part.] One of the 

 large cells formed after the primary 

 divisions of a developing ovum 

 (emb.\ 



meganucleus (mgg'anu'kleus) n. [Gk. 

 megas, large ; L. nucleus, kernel.] 

 The larger nucleus, or vegetative 

 nucleus, of the Infusoria (zool.). 



megasclere (mSg'askler) n. [Gk. 

 megas, large ; skleros, hard.] A 

 skeletal spicule of the general 

 supporting framework, as opp. a 

 microsclere (zool.). 



megaspherlc (mgg'asfeVlk). Megalo- 

 spheric. 



megasporangium (me'g'asporanjium) 

 n. [Gk. megas, large ; sporos, 

 seed; anggeion, vessel.] A macro- 

 spore-producing sporangium (bot.). 



megaspore (me'g'aspor) n. [Gk. 

 megas, great ; sporos, seed.] A 

 larger-sized spore of dimorphic 

 forms in reproduction by spore- 

 formation (zool.) ; the larger spore 



