HEART IX PETROMYZOX. ^37 



Explanation of Figures. 



Complete list of reference letters. 



a. anus. 



(to. aorta. 



a.v. auricnlo-ventricular septum. 



hp. blastopore. 



hr.i. branchial invagination. 



liv.c. branchial cleft. 



ch. chorda dorsalis. 



e.jn.j). external mouth-pit. 



end. endocardium. 



ej). epiblast. 



fjj. fore-gut. 



//. heart. 



hij. hypoblast. 



l.m. lateral plates of mesoblast. 



l.j). labial protuberance. 



m. mouth. 



rnc.a. mesocardium anterius. 



rnc.p. mesocardium posterius. 



vij/. mid-gut. 



7ii.[ll>. splanchnic plate of mesoblast. 

 n. neural cord. 



p.c. pericardium. 

 ])u.t. pronephric tubule. 

 j>.p.c. pleuro-peritoneal cavity. 

 jKjhm. pleuro-peritoneal membrane. 

 s.ch. subchorda. 

 s.in. somatic mesoblast. 

 t.a. truncus arteriosus. 

 tv.d. Wolffian duct. 

 a\ mesenchyraatous cells. 



1/e. yolk-cells. 



