452 MORGAN. 



DESCRIPTION OF PLATE XXV. 



Fig. 13. Section through wall of young larva (Fig. 5), showing beginning of 

 proboscis vesicle, v. 



Fig. 14. Next section in same series. 



Fig. 15. Optical section of anterior enteroccel and proboscis vesicle, v. Older 

 than last. 



Fig. 16. Optical section. Same, but older. 



Fig. 17. " " of still older organs. 



Fig. 18. " " of enteroccel, vesicle, and heart, h, of larva of Fig. 6. 



Fig. 19. Longitudinal section through 18 in plane of paper. 



Fig. 20. Section through Fig. 17 at line a. 



Fig. 21. " " " " b. 



Fig. 22. " " " " c. 



Fig. 23. " "18 " d. 



Fig. 24. " " " " e. 



Fig. 25. " " " " / 



Fig. 26. " " " " g. 



Fig. 27. Section through side wall of stomach to show origin of the first paired 

 body cavities, second pair of enteroccels, collar body cavities, be 1 . 



Fig. 28. Section to one side of last. 



Fig. 29. Section to other side of last. 



Fig. 30. Section through side wall of stomach of still younger stage than Fig. 27. 



Fig. 31. Section through older stage than Fig. 27. All connection with digestive 

 cells lost. 



Fig. 32. Section through last paired body cavities, be 3 , showing their origin. 



