Sudler. — Penilia. 
Fig. 7. 
Fig. 8. 
Fig. 9. 
Fig. 10. 
Fig. 11. 
Fig. 12. 
Fig. 13. 
Fig. 14. 
Fig. 15. 
Fig. 16. 
Fig. 17. 
Fig. 18. 
Fig. 19. 
Fig. 20. 
Fig. 21. 
Fig. 22. 
Fig. 23. 
Fig. 24. 
PLATE 2. 
Two-cell stage of the segmenting egg. 
Fonr-cell stage. 
Eight-cell stage. 
Sixteen-cell stage. 
Thirty-two cell stage. 
Sixty-four cell stage (section). 
Section of egg having about one hundred and twenty-eight cells and 
showing the beginning of gastrulation. 
A more advanced stage of the same process. 
A still older stage showing the gastrula mouth at its greatest degree 
of development. 
A section of a larva having all three germ layers differentiated. 
A horizontal section of a larva which has the first rudiments of the 
two most anterior appendages. 
Ventral view of an embryo whose outward form is beginning to 
change. 
An older stage than the preceding seen from the ventral surface and 
showing the first traces of the first antennae. 
An older stage seen from the ventral side and showing the broaden¬ 
ing at the anterior end and elongation of the embryo. 
An embryo seen from the ventral side showing the first and second 
antennae and rudiments of the mandibles. 
An embryo with the first three pairs of appendages clearly defined 
and a maxillary region marked off seen from the ventral side. 
A transverse section just behind the second antennae of a stage cor¬ 
responding with Fig. 21. 
A transverse section of the same embryo nearer the head. 
