450 MORGAN. 



DESCRIPTION OF PLATE XXIV. 



Fig. i. Youngest larva caught, seen from side view. 



Fig. 2. Same, seen from behind. 



Fig. 3. Same, seen from front. 



Fig. 4. Enlarged view of apical plate and enteroccel of same larva. 



Fig. 5. Older larva than last. Proboscis vesicle, v, and paired body cavities 

 appear. Right side shown in figure. 



Fig. 6. Fully formed Tornaria. Left side shown in figure. 



Fig. 7. Apical plate, with eyes and ciliated band of last. Seen from above. 



Fig. 8. Oesophagus and three pairs of gill pouches of larva in Fig. 6. Seen from 

 above. 



Fig. 9. Young Balanoglossus. Seventy hours older than Fig. 6. Alcoholic spec- 

 imen. 



Fig. 10. Apical plate of Nassau larvae. Seen from above. 



Fig. 11. Side view of part of Nassau larva, showing longitudinal band, and/, 

 and circular band, cb, also the anterior lateral and middle lateral areas. 



Fig. 12. Part of Nassau larva, seen from in front, with digestive tract seen through 

 body walls; also longitudinal and circular bands. 



