426 EDGAR J. ALLEN. 



Fig. 15. — Horizontal section through anterior end of cephalic aorta of 

 larva slightly older than that of Fig. 14. x 240. 



Fig. 16, a, b. — Transverse sections of dorsal sac and aorta of Palsemonetes 

 larva, a few hours old. X 240. 



Fig. 17. — Transverse section through posterior portion of dorsal sac of 

 Palajmonetes larva, three weeks old. X 240. 



Fig. 18. — Transverse section of just-hatched larva of Palsemonetes, through 

 front end of pericardium, x 240. 



Fig. 19. — Ditto through middle of pericardium, x 240. 



