24, Figure 7, and Sheet 2, Figure 2.

Figure 3. Side view of the pericardium.

a.br., afferent branchial artery.
a.c.s., anterior cardinal sinus (= internal jugular vein).
au., atrium (auricle) (= the two auricles of higher forms).
b.a., bulbus arteriosus.
c.a., conus arterious.
cd. a., caudal artery.
cd.v., caudal vein.
c.s., Cuvierian sinus.
d.a., dorsal aorta.
E., eye.
e.br., efferent branchial arteries.
g.s., in position of gill slits.
h.br.a., hypobranchial artery.
H.S., hepatic sinus.
[i.j.s., inferior jugular sinus (= external jugular vein).]
K., kidney.
L.V., lateral vein.
[oe.s., ventral wall of oesophagus.]
P.C.C., pericardial cavity.
P.C.S., posterior cardinal sinus.
p.p.c., pericardio-peritoneal canal.
P.V., portal vein.
r.p.v., reno-portal vein.
s.c.v., subclavian vein.
Vn., ventricle.
-v.s.v., inferior (= external) jugular vein-.

Figure 4. Skeleton of pectoral limb, and girdle.--
g., the girdle (also in Figure 3).
m.p., meso-pterygium.
mt.p., meta-pterygium.
p.p., pro-pterygium.
sc., its dorsal portion.

{Illustration: Diagram Sheet 16.}

Sheet 17

-The Uro-genital Organs of the Dog-Fish_.

Figure 1. The Female, the oviduct of the left side cut away, -and an
egg case in the oviduct.-

Figure 2. The Male.

The rectum is removed in both cases, and the silvery peritoneum
dissected off from the kidneys.

Figure 3. A generalized diagram of the uro-genital organs.--
All references in text.
Ms., the mesonephros, is the epididymis in the male, and is reduced
in the female; Ms.d., its duct, is the vas deferens in the male, and
persists only as the urinary receptacle in the female.
Mt. and Mt.d., the metanephros and metanephric duct, become the
functional kidney and ureter in both sexes. G. is the gonad
(reproductive gland), and M.L. the animal's middle line (median
plane).
-Ps.-, [Pr.,] the pronephros, is never developed in the Dog-fish;
P.d., its supposed duct, is the oviduct of the female, and is
suppressed in the male.

{Illustration: Diagram Sheet 17.}

Sheet 18.

Figure 1. The Dog-Fish Brain, dorsal view.

Figure 2. Median section of the same. To the right a more
diagrammatic figure. The nerves are numbered:--
[BR1, BR2, BR3, BR4 branches of X forking over the second to the
fifth gillslit.]
cb., cerebellum.
h.s.c., horizontal semi-circular canal of ear, exposed by the slicing
down of the otic mass.
[LAT., lateral-line branch of X.]
m.o., medulla oblongata