Figure 2. Simplified and more typical fish circulation, in which the posterior cardinals have not coalesced in the median line. The Cuvierian veins = the vena cava superior of the higher type; the posterior cardinal is represented by the azygos vein in the Rabbit. Compare Sheet 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.