ACTINOLOGICAL STUDIES. 311 



EXLANATION ON PLATE XX. 



Reference Letters: — d., directive mesenteries; 

 n.dJ' non-directive mesenteries of the first cycle; n.d. n < 

 non-directive mesenteries of the second cycle ; i u ' i Uh i lv 

 and i v > incomplete mesenteries of the second, third, fourth 

 and fifth cycle respectively; as., oesophagus; as. g., 

 oesophageal grooves. 



Fig. 1. Diagrammatic T. S. showing the arrangement of 

 mesenteries in the typical specimen. The 

 first cycle of mesenteries is shown complete, 

 and the arrangement of the remaining mesen- 

 teries is represented in one-sixth part only. 



Fig. 2. Diagrammatic T. S. illustrating the condition 

 found in the specimen with a single oesophageal 

 groove, and four pairs of mesenteries of the 

 second cycle complete, and two incomplete. 



Fig. 3. Diagrammatic T. S. illustrating the arrangement 

 of mesenteries in the specimen with three 

 oesophageal grooves. 



Figs. 4 and 5. Diagrammatic T. Ss. showing the 

 arrangement in the two specimens where the 

 relative situations of the oesophageal grooves 

 were abnormal. 



