326 Scientific Proceedings, Royal Dublin Society. 



Plate V. 



Fig. 1. — Horizontal section through a mesentery of Bunodes thallia. 



Fig. 2. — Vertical section through a portion of body wall, oral disk, and 

 protruded oesophagus of B. verrucosa, showing the warts, 

 circular muscle, and the muscular pleating immediately sur- 

 rounding the mouth. 



Fig. 3. — Vertical section through the circular muscle of B. verrucosa. 



Fig. 4. — Transverse section of a very young specimen of B. verrucosa. 

 The section was taken at such a level that the pairs of 

 "secondary" mesenteries which appeared last (those on 

 either side of the directive mesenteries near the top of the 

 figure) are just visible as prolongations inwards of the 

 mesoderm into the endoderm. 



Fig. 5. — Half a transverse section through a young specimen of Tealia 

 crassicornis, showing the regular pentamerous arrangement 

 of the mesenteries. The primary pairs of mesenteries are 

 marked i., the secondary pairs n., and at the top of the 

 figure two tertiary pairs are marked in. The section was 

 rather oblique, the upper end of the figure being nearer to 

 the oral disk than the lower. 



