420 LEFEVRE. 
EXPLANATION OF PLATE XXX. 
The test is only shown in Figs. 6 and 7, and in Figs. 9-15 the ectoderm is 
represented merely by a line. The elements of the blood have not been drawn in 
Figs. 10-15. 
Fic. 6. Transverse section of stolon, showing double-walled partition, /¢. 
X 500. 
Fic. 7. Transverse section of stolon at point where a bud is beginning to 
form. The ectoderm on one side is thickened, and the double-walled partition is 
much thickened and dilated. X 500. 
Fic. 8. Transverse section through a very young bud-rudiment and stolon, at 
about the stage of Fig.1, Pl. XXIX. The walls of the partition are coming 
together to close off the inner vesicle, 7.v. Blood cells are found lying against 
the outer surface of the latter. X 500. 
Fic. 9. Transverse section through posterior end of a bud-rudiment at about 
the stage of Fig. 3, Pl. XXIX, showing thick wall of inner vesicle on right side, 
y.w.in.v., and beginning of pericardial rudiment, fc.7. X 500. 
Fic. 10. Transverse section through posterior end of a young bud, showing an 
early stage in the displacement or shifting of the inner vesicle. The wall of the 
latter is being bent in at the point indicated by the line a. X 200. 
Fic. 11. Transverse section through posterior end of bud slightly older than 
last, showing further progress of the displacement of the vesicle. The pericardial 
rudiment, fc.7., is at a much lower level than in the last figure, and the wall of 
inner vesicle is being bent in further at a; this is the fold which will form the left 
peribranchial sac, f/.f4.5. X 200. 
Fic. 12. Transverse section through the middle region of same bud as the 
one shown in Fig. 11. The section lies in front of the connection with the sto- 
lonic partition, and shows the beginning of the fold which will form the right peri- 
branchial sac, f7.p4.s. The rudiment of dorsal tube, @.47., is also shown. X 200. 
Fic. 13. Transverse section through the anterior end of a bud slightly older 
than Fig. 9. The rudiment of the dorsal tube is shown, and consists at this stage 
of a few scattered cells, adhering to the wall of the inner vesicle a little to the left 
of the median dorsal line, d.4.7. The difference in thickness between the right 
side and the rest of the vesicle is seen to be but slight in this region. X 200. 
Fic. 14. Median sagittal section of a bud at about the stage of Fig. 4, Pl. 
X XIX, showing the position and extent of the dorsal tube, d.¢. The peribranchial 
cavity is not yet completely constricted off from the branchial sac. X 200. 
Fic. 15. Transverse section through the extreme posterior end of a bud, 
showing the origin of the gut, g¢.7., asa diverticulum on the left side of the 
branchial sac. X 200. 
