Sutler. — Penilia. 
Fig. 25. 
Fig. 26. 
Fig. 27. 
Fig. 28. 
Fig. 29. 
Fig. 30. 
Fig. 31. 
Fig. 32. 
Fig. 33. 
Fig. 34. 
PLATE 3. 
An embryo seen from the ventral side and which has five pairs of 
thoracic appendages in addition to those seen in Fig. 22. 
A slightly older stage seen from the left side. 
Ventral view of an embryo, at a stage when both the first and second 
maxillae are present. 
Ventral view of an older larva. In this specimen the shell (Sh.) has 
assumed quite definite proportions. 
An embryo that has assumed somewhat the size and relations of 
parts as seen in the adult, seen from the ventral side. 
A horizontal section of an embryo at a stage a little older than repre¬ 
sented by Fig. 21. 
A horizontal section of an embryo somewhat younger than that seen 
in Fig. 25. 
A horizontal section to show the arrangement of entoderm, meso¬ 
derm, and ectoderm of the thoracic region at a stage represented 
by Fig. 26. 
A section through the anterior dorsal angle of an embryo showing 
the cervical gland at the stage of its maximum development. 
A transverse section of an embryo at a stage corresponding to Fig. 28 
to show the heart, intestine, and shell-glands. 
