206 BULLETIN OF THE 



Fig. 6\ Serrated spine of parapodium. 



7. Larva of Mejj/ttfiijs oldor tlian die last. View from the dorsal side. 



" 8. Tlie same. View from tiie ventral side. 



9. Larva of Nepldhys in wliich tlie cephalic tentacles have begun to form. 



" 10. The same. View from the dorsal side. 



" 11. Still older larva. 



" 12. Oldest larva of A\7;/i%s. 



" 12*. Head of tlie same. 



" 12''. Parapodium of fourth segment. 



" 13. Larva of JIarmothoc {i). 



" 13'. The same seen from above. 



" 14. Youngest larva, iomul o{ Lepidonotus squamatus. 



15. The same, more advanced in growth (lateral view). 



" 16. More advanced stage of Lepidonotus than the last (dorsal view). 



" 17. The same (ventral view). 



" 18. Telotrochal larva allied to the young of Pohjgordius. 



PLATE V. 

 Pilidium (?) and Tornaria. 

 a. Anterior end of the worm. 

 CO. External opening of the cephalic sac. 

 cs. Cephalic sac. 

 dp. Dorsal pore. 



i. Invagination in the lateral wall of the larva. 

 m. Mouth. 

 ce. (Esophagus. 



r. Half-absorbed remnant of the larva. 

 s. Stomach. 

 lu t. Water vascular system. 



Fig. 1. Youngest Nemertean larva with well-developed oesophagus and stomach. 



" 2. Dorsal view of the same. 



" 3. Older larva with extended snout. 



" 4. Larva still older than the last. 



" 5. Dorsal view of the same. 



" 6. Older larva with lengthened proboscis. 



" 7. Larva just before the extrusion of the worm. 



" 8. Larva of the same age as that shown in Fig. 3, yet without cephalic sacs. 

 " 9, 10. Larva just before the birth of the contained Nemertean. 



" 11. Young worm just transformed from the larva. 



" 12. Dorsal view of the same. 



" 13. Side view of tlie last. 



" 14. An older Nemertean which probably developed from the last. 



" 14*. Proboscis, seen from below. 



" 14*. The same, from one side. 



" 15. Critical stage in the metamorphosis from the original larva. 



" 16. Youngest Tornaria found at Newport. 



" 17. Still more mature Tornaria, also from Newport. 



