ON THP^ DEVRLOPMRNT OF SAGITTA. 397 



Fig. 13.— S. bipunctata. Longitudinal iiorizoutal section ilirougli a late 

 curled embryo, cutting tlie bead and trunk, x 375. 



Fig. 14. — Section tbrough tbe same embryo, showing the genital cells 

 below and the tail above. The embryo is cut twice owing to curvature, 

 X 375. 



Fig. 14 o. — ^Diagrani to show the planes of section of Figs. 13 and 14. 



Fig. 15. — S. bipunctata. Section of embryo at about the same stage as 

 Figs. 13, 14, showing the genital cells and their envelopes, x 900. 



PLATE 20. 

 Fig. 16. — S. bipunctata. Larva just after hatching, x 200. 

 Fig. 17.— S. enflata. First day. Genital cells, x 500. 

 Fig. 18. — S. enflata. Fourth day. Ventral view. The eyes are seen 

 through the bead, x 200. 



Fig. 19. — S. enflata. Fourth day. Head and neck, lateral view showing 

 parenchyma, x 600. 



Fig. 20. — S. enflata. Third day. Genital region in stained specimen, 

 showing envelopes of genital cells, x 800. 



Fig. 21. — S. enflata. Fourth day (a late specimen). Showing migration 

 of genital cells, X 600. 



Fig. 22. — S. enflata. Second day. Transverse section of head, x 

 1000. 



Fig. 23. — S. bipunctata. Third day. Transverse section of head. 

 Only half of the section is represented, x 900. 



Figs. 24 — 26. — S. enflata. Three sections through the head of a sixth- 

 day larva, x 375. 



Fig. 24. — Through the mouth. 



Fig. 25. — Througii the eyes and beginning of the pharynx. 

 Fig. 26. — Through the crescent-shaped transverse muscle in the 

 posterior part of the head. 



Figs. 27 — 29. — Three sections through the head and neck of a ninth- 

 day enflata larva. X 375. 



Fig, 27. — Through the posterior region of the iiead. 

 Fig. 28. — Through the beginning of the neck. 

 Fig. 29.— Through the neck. 



