EXPLANATION OF THE LETTERING. 481 



th.n Thoracic nerve cord. 



th.so Mesoblastic somites of thoracic metameres. 



t.l Remnants of ingested larval tentacles. 



t.l.n Thoracic temperature organs. 



t.p Telopore. 



tr Trabecute 



tr.c Trabeculse cranii. 



t.st Tendinous stigmata. 



u Point of union of vascular canals. 



V Ventricle; subneural gland; vestibule. 



v.c Vascular canals. 



v.d Vas deferens. 



v.dec Vagus decussation. 



v.fd Ventral wall of anal frill. 



vg Vagus (yellow body). 



vg.ap Vagus appendages. 



vg.n Vagus nerves. 



vg.mn Vagus neuromeres. 



v.l Vascular layer. 



v.m Ventral margin. 



w.d WolflBian duct. 



yk.c.h Yolk cells of head. 



yk.c.t Yolk cells of tail. 



yk.nav Yolk navel. 



