1903] On the Nemerteans of Norway. 35 



Plate IL 



Fig. 16 (a — d). Diagrams illustrating the evolution of the body wall 

 of Heternemerteans. 



a. Carinella stage. 



b. Carinoma stage. 



c. Primitive Lineid stage. 



d. Specialized Lineid stage. 



For explanation vide text p. 15. 

 Fig. 17 — 22. Schematic reconstructions through the anterior end 

 of several Lineids. The buccal vascular vessels, the 

 oesophageal nerves, together with the proboscis and its 

 sheath have for the sake of simplicity been omitted. 

 The oesophageal vascular lacunae have also been repre- 

 sented as simple vessels, instead of the network round the 

 ventral surface of the oesophagus which really exists. 

 An asterisk* denotes the point where the median dorsal 

 blood vessel leaves the proboscis sheath. 

 Fig. 17. Micrura atra, x 10. 



„ 18. Micrura bergenieola, x 10. 



„ 19. Linens einerens, x 5. 



„ 20. Linens scandinaviensis, x 10. 



„ 21. Cerebratulus norvegicus, x 10. 



,, 22. Cerebratulus longifissus, x 5. 



