THE NOTOCHORD AND ALIMENTARY CANAL 453 
N. Ne. 
l 
Fie. 167.—A, Diagram or Sxcrion THROUGH A TRILOBITE-LIKE ANIMAL; B, 
DiaGRaM TO ILLUSTRATE THE SUGGESTED FoRMATION oF THE NorocHorD 
FROM A VENTRAL GROOVE; OC, DiaGRAM TO ILLUSTRATE THE SUGGESTED 
ForMaTIon OF THE Post-BrancHIAL GUT BY THE CONTINUATION OF THE SAME 
PROCESS OF VENTRAL GROOVE-FORMATION, COMBINED WITH OBLITERATION OF 
APPENDAGES AND GrowrH oF PLEURAL Foxtps; D, Diacram To ILLUSTRATE 
THE COMPLETION OF THE VERTEBRATE TyPE By THE MEETING OF THE PLEURAL 
Foips In tHe Mip-VenrraL LIne with THE OBLITERATION OF THE ATRIAL 
CaVITY AND THE CONVERSION OF THE VENTRAL GROOVE INTO THE CLOSED 
ALIMENTARY CANAL, 
Al., alimentary canal; N., nervous system; My., myotome; Pl., pleuron; App., 
appendage; Neph., nephrocele; Met., metaccele; Sd., segmental duct; Mes., 
mesonephros; At., atrial chamber; Ne¢., notcchord; H., heart; F., fat body ; 
Ng., notochordal groove. (These diagrams are intended to complete the 
diagrams on p. 413, which, as stated there, were purposely left incomplete.) 
. 
