480 EXPLANATION OF THE LETTERING. 



proc Procephalon. 



prosen Prosencephalon. 



pr.s Primitive sheath. 



prt Protoplasm. 



ps Posterior sclerotics; pancreas. 



p.s.o Primitive sense organs. 



pt Pituitary gland or duct. 



p.t Primary tentacles. 



p.t.r Posterior triangular recess. 



p.v Posterior median ventral plate; postorbital line of canal 



organs. 



pv.l Pulsatile vessel. 



p.v.t Mass of bony trabeculae below the postorbital valley. 



r Ridges; roots to spinal nerves; rostrum. 



r.d. . . . , Visual rods. 



r.l Rostral line ot canal organs. 



rost Rostrum. 



r.s Shelf plate on the inner surface of the rostrum. 



s Scales; sulcus on the tioor of the procephalic lobes; stomach. 



s.c Superficial canals; sensory canals. 



s.c.n Segmental cardiac nerve. 



s.c.no Subcortical neuropile. 



s.d Sucking disc. 



s.g Shell gland. 



s.l Superficial layer. 



S.l.c Cells derived from sheath of Jateral cords. -> 



s.lch Sheath to lemmatochord. 



S.m.n Sheath to median nerve. ^ ,:>' 



sn.c Sensory canals. "?■' 



s.o Suborbital plates; sense organs. 



S.o.l Supra-orbital line of canal organs. 



sp Spindle-shaped dilatation on the sensory tubes; subdermal 



process on lateral margin of premaxillse. 



st Stomach; stomodasum. 



s.t Sensory tubes. 



st.c. or st.co Stomodaeal commissure. 



st.g Stomodaeal ganglion. 



st.n Stomodaeal nerves. 



sto Stomodaeum; stolon. 



t Terminal joint to cephalic appendages; testis. 



t.b Tongue bar. 



t.cl Telocoele. 



t.cx Tergo-coxal muscles. 



t.d Tear duct; thoracic duct. 



telbl Teloblasts. 



telen Telencephalon. 



tel.o Telopore. 



t.g Groove (for tentacle?). 



tg.prpl Tergo-proplastral muscles. 



th Thyroid. 



th.ap Thoracic appendages. 



