EXPLANATION OF THE LETTERING. 475 



c.r. .Root-like cephalic outgrowths. 



cran Cranium. 



cr.g. ... .Cranial ganglia. 



cu.d . Cuvierian duct. 



cut . . Cuticular layer. 



c.w . . Circle of Willis. 



cx.g . .Coxal glands. 



cx.t. . Coxo-tergal muscles. 



d. and d 1 . .Dorsal plate; dentine, or dentine-like chiten. 



d.bl. . . . . Dorso-branchial line of canal organs. 



d.c .Sensory and glandular ducts. 



d.end ; or d.e . Ductus endolymphaticus. 



d.f .Dorsal fins. 



d.fd .Dorsal portion of anal frill. 



di.c Dicephalon. 



di.enc Diencephalon. 



d.o .Dorsal organ; dorsal opening in cephalic shield; cephalic 



navel. 



dor.o Dorsal organ. 



d.s . .Dorsal sclerotic plate. 



dt. and dt 1 .Denticles or denticle-like spines. 



e. and e 1 .Mesethmoid; enamel layer or enamel-like chiten; ocelli. 



e.b.m. . . . .External branchial muscle. 



ec. . Ectoderm. 



ec.d . Excretory duct. 



ec.pa.e Ecto-parietal eye. 



el .External labials (Drepanaspis); extra-laterals; suborbitals. 



en 1 .Primitive gastrula; cephalic endoderm. 



en . . Endoderm of trunk. 



en.ch . Endochondrites. 



encl Endocrele. 



en. ex. . Entocoxal nerves. 



en.me.cl Endomesoccele. 



en.pa.e. . . . Endoparietal eye. 



ent . . Entapophyses. 



ep. or eph. . . .Epiphysis; parietal eye tube. 



e.t ... .Parietal eye tube. 



ex.p . External pores. 



ext.g. . . .External gills. 



f.br Forebrain. 



flab, or fl Flabellum. 



f .p Fringing plates. 



f.r Free nerve endings; frontals; fleshy portion of the rostrum 



g Gills; gastrula; germ cells. 



g.ar .Gill arches. 



gast Gastrula 



g.c Germ cell. 



g.ctr. or g.c Gustatory center; gustatory tracts. 



g.c.tr General cutaneous tracts. 



g.cut General cutaneous nerves. 



g.g Gustatory ganglia. 



