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' 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' Denticles or denticle-like spines. 



e. and e' 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' Primitive gastrula; cephalic endoderm. 



en Endoderm of trunk. 



en.ch Endochondrites. 



end Endoccele. 



en.cx Entocoxal nerves. 



en.me.cl Endomesocoele. 



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. 



