_al._ Alimentary tract. _an._ Point where anus will be formed. _ao._ Dorsal
aorta. _ar._ Rudiment of anterior root of spinal nerve. _b._ Anterior fin.
_c._ Connective-tissue cells. _cav._ Cardinal vein. _ch._ Notochord. _df._
Dorsal fin. _ep._ Epiblast. _ge._ Germinal epithelium. _ht._ Heart. _l._
Liver. _mp._ Muscle-plate. _mp´._ Early formed band of muscles from the
splanchnic layer of the muscle-plates. _nc._ Neural canal. _p._ Protoplasm
from yolk in the alimentary tract. _pc._ Pericardial cavity. _po._
Primitive ovum. _pp._ body-cavity. _pr._ Rudiment of posterior root of
spinal nerve. _sd._ Segmental duct. _sh._ Cuticular sheath of notochord.
_so._ Somatic layer of mesoblast. _sp._ Splanchnic layer of mesoblast.
_spc._ Spinal cord. _sp.v._ Spiral valve. _sr._ Interrenal body. _st._
Segmental tube. _sv._ Sinus venosus. _ua._ Umbilical artery. _um._
Umbilical cord. _uv._ Umbilical vein. _V._ Splanchnic vein. _v._
Blood-vessel. _vc._ Visceral cleft. _Vr._ Vertebral rudiment. _W._ White
matter of spinal cord. _x._ Subnotochordal rod (except in fig. 14_a_). _y._
Passage connecting the neural and alimentary canals.