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 floor 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 lateral 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 premaxilke. 



st .Stomach; stomodaeum. 



s.t ... -Sensory tubes. 



st.c. or st. co . Stomodseal commissure. 



st.g. . Stomodseal ganglion. 



st.n . . Stomodaeal nerves. 



sto. . . .Stomodaeum; stolon. 



t .Terminal joint to cephalic appendages; testis. 



t.b. .... .Tongue bar. 



t.cl .Teloccele. 



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. 



