432 
ALFRED GIBBS BOURNE. 
EXPLANATION OP PLATE XXIX, 
Illustrating Dr. A. G. Bourne’s Paper “ On the Supposed 
Communication of the Vascular System with the Exterior 
in Pleurobranchus.” 
Fig. 1 . — Pleurobranchus testudinarius. Dorsal view of a specimen 
from which the mantle-flap and a portion of the dorsal integument have been 
removed by cutting along the surface m. per. Pericardium, vent. Ventricle. 
aur. Auricle, an. Anus. br. ctenidium (gill), g. External genital organs. 
x. Orifice of the glandular sac. re. The orifice of the renal sac lies in this 
direction underneath the gill. 
Fig. 2.— Aplysia limacina. Similar view. Other letters as in Fig. 1. 
x. Orifice of the grape-shaped gland, g. Genital groove, g. p. Genital pore. 
Fig. 3. — Diagram of the relation of the glandular sac to the pericardium 
and auricle, gl. The glandular sac. x. Its orifice. br. The ctenidium. 
br. v. The branchial vein. au. The auricle, v. The ventricle, ao. The aorta. 
per. Pericardium, w. The wall separating the lumen of the glandular sac 
from that of the auricle' and branchial vein, composed in reality of three layers, 
the wall of the sac, the pericardial wall, and the auricular wall, which together 
form a single exceedingly thin membrane. 
Fig. 4. — The glandular sac, as seen from the lumen of the auricle, x. Its 
orifice. 
Fig. 5. — Longitudinal section of the sac passing through its orifice x. 
ep. Epidermis, c. The neck of the sac. gl. ep. The glandular epithelium 
lining its walls, a. Gland-cells, showing deeply-stained contents, c. t. Con- 
nective tissue, to. The exceedingly thin wall separating the lumen of the 
sac from that part of the auricle. 
Fig. 6. — A portion of the glandular epithelial wall of the sac more highly 
magnified, a. Gland-cells with contents, b. Other cells, ci. Cilia, m. 
Highly refracting margin, p. Pigment, c. t. Connective tissue. 
