GP. 
SIOsrs 
10. 
11. 
12. 
12°. 
12». 
13. 
13%. 
14. 
15. 
16. 
17. 
18. 
BULLETIN OF THE 
Serrated spine of parapodium. 
Larva of Nephthys older than the last. View from the dorsal side. 
The same. View from the ventral side. 
Larva of Nephthys in which the cephalic tentacles have begun to form. 
The same. View from the dorsal side. 
Still older larva. 
Oldest larva of Nephthys. 
Head of the same. 
Parapodium of fourth segment. 
Larva of Harmothoé (+). 
The same seen from above. 
Youngest larva found of Lepidonotus squamatus. 
The same, more advanced in growth (lateral view). 
More advanced stage of Lepidonotus than the last (dorsal view). 
The same (ventral view). 
Telotrochal larva allied to the young of Polygordius. 
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. 
@. Césophagus. 
r.  Halfabsorbed remnant of the larva. 
s. Stomach. 
wt. Water vascular system. 
Youngest Nemertean larva with well-developed esophagus and stomach. 
Dorsal view of the same. 
Older larva with extended snout. 
Larva still older than the last. 
Dorsal view of the same. 
Older larva with lengthened proboscis. 
Larva just before the extrusion of the worm. 
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. 
itil 
Young worm just transformed from the larva. 
Dorsal view of the same. 
Side view of the last. 
An older Nemertean which probably developed from the last. 
Proboscis, seen from below. 
The same, from one side. 
Critical stage in the metamorphosis from the original larva. 
Youngest Yornaria found at Newport. 
Still more mature Tornaria, also from Newport. 
