416 
LEFEVRE. 
DESCRIPTION OF THE PLATES. 
All the drawings have been made with a camera lucida. The lenses used were 
those of Zeiss, and the magnification is given after the description of each figure. 
REFERENCE LETTERS. 
anus. 
ampulla. 
blood sinus of stolon. 
“branchial orifice. 
branchial sac. 
branchial wall. 
cavity of rudiment of sexual 
organs. 
cloaca or atrium. 
cloacal orifice. 
cavity of pericardial rudi- 
ment. 
stolonic double- 
walled partition. 
cells of cellulose test. 
dorsal tube or hypophysis. 
rudiment of dorsal tube. 
thickened dorsal wall of peri- 
branchial sac, which invagi- 
nates to form the heart. 
ectodermal invagination to 
cavity of 
form the branchial orifice. 
ectoderm. 
ectodermal invagination to 
form the cloacal orifice. 
endostyle. 
fold which forms left peri- 
branchial sac. 
fold which forms right peri- 
branchial sac. 
genital cord. 
ganglion. 
rudiment of ganglion. 
rudiment of sexual organs. 
branchial stigmata or gill 
slits. 
rudiment of branchial stig- 
mata. 
digestive tract. 
rudiment of digestive tract. 
Tudiment of heart. 
int. 
in.U. 
SEL: 
l.d.t. 
Lp.ex. 
l.pb.s. 
M2.C 
ml.c. 
0.€. 
0.7. 
V.ACX. 
7 .p.ex. 
r.pb.s. 
7.SU.C. 
7 .W.1N.Us 
st. 
St.C. 
intestine. 
inner or primitive vesicle. 
anterior extension or pouch 
of left peribranchial sac. 
lumen of dorsal tube. 
posterior extension or pouch 
of left peribranchial sac 
(left epicardial sac ?). 
left peribranchial sac. 
free amoeboid cells of blood. 
muscle-cells. 
oesophagus. 
“organe réfringent” or py- 
loric gland. 
duct of “organe réfringent.” 
rudiment of “organe réfrin- 
gent.” 
peribranchial wall. 
pericardium. 
pericardial rudiment. 
double-walled partition or 
cloison of stolon. 
anterior extension or pouch 
of right peribranchial sac. 
posterior extension or pouch 
of right peribranchial sac 
(right epicardial sac ?). 
right peribranchial sac. 
remnant of connection be- 
tween the stolonic partition 
and left peribranchial sac. 
thickened wall of inner vesi- 
cle on right side. 
stomach. 
connection of stolonic parti- 
tion with inner vesicle or 
with left peribranchial sac. 
wall of stomach on anterior 
side. 
stolon. 
cellulose test. 
