478 EXPLANATION OF THE LETTERING. 



m.n.co Median neural commissure. 



m.oc Median ocellus. 



mp Malpighian tubules; madreporite. 



m.pl Medullary plate. 



m.r Marginal wall or ridge. 



ms. . . . , Mesoderm. 



msc Mesenchyme. 



ms.en Mesentoderm. 



m.s.p.ent Mesoplastro-entapophyseal muscle. 



m.t Motor nerve tubes. 



mt Mantle. 



mx Maxillae. 



mx.d Excretory duct to maxillary segment. 



mxl Maxillaria. 



n. or n.c Nerve cord; neuron; neuromere. 



n.ch.c Neurochordal canal. 



n.co Neural commissure. 



n.cr Neural crests. 



neph Nephridia. 



neu.p Neuropore. 



n.l Neural lamina of cephalic shield. 



n.n Neural nerve. 



noto Notochord. 



n.p Neuropile; neural process; neural plate; neuropore. 



np.d Nephric duct. 



n.r Nerve ring. 



n.st Primitive mouth; neurostoma 



n.tr Neural tracts. 



n.v Neural vessel. 



o.b Opening to branchial chamber. 



oc Ocelli; occipital plate. 



o.c Occipital line of canal organs. 



oc.f Occipital foramen 



od Oviduct. 



oe (Esophagus. 



ol Primitive olfactory organ; frontal organ. 



ol.l Olfactory lobes. 



ol.l.n Lateral nerve of olfactory organ. 



ol.m.n Median nerve of olfactory organ. 



ol.np Olfactory neuropile. 



ol.o Olfactory organ. 



ol.r Olfactory recess. 



ol.v Ventricle of olfactory lobes. 



o.m Circumoral membrane. 



op Operculum. 



o.p Postorbital valley. 



op.g Optic ganglion. 



op.neu Optic neurones. 



op.pl Optic plate; opercular pleurite. 



op.s Opercular segment. 



op.tr Optic tracts. 



