Page:First course in biology (IA firstcourseinbio00bailrich).pdf/353

 liver large or small? Simple or lobed? The spleen (mi, Fig. 220) lies in a loop of the intestine. The last part of the intestine is straight and is called the rectum. Is it of the same size as the other portions of the intestine? The fish does not possess a pancreas, the most important digestive gland of higher vertebrates.

(See also colored figure 4.)

bf, barbels on head (for feeling); h, ventricle of heart; as, aortic bulb for regulating flow to gills; vk, venous sinus; ao, dorsal aorta; ma, stomach; l, liver; gb, gall cyst; mi, spleen; d, small intestine; md, large intestine; a, vent; s, s, swim bladder; ni, ni, kidney; hl, ureter; hb, bladder; ro, eggs (roe); mhe, opening of ducts from kidney and ovary.

Questions: Are the kidneys dorsal or ventral? The swim bladder? Why? Why is the swim bladder double? Does blood enter gills above or below?

The ovary lies between the intestine and the air bladder. In Fig. 220 it is shown enlarged and filled with egg masses called roe. It opens by a pore behind the vent. The silver lining of the body cavity is called the peritoneum. (See Chap. VII, Human Biology.)

Is the air bladder simple or partly divided in the perch? In the carp? (Fig. 220.) Is it above or below the center of the body? Why? The air bladder makes the body of the fish about as light as water that it may rise and sink with little effort. When a fish dies, the gases of decomposition distend the bladder and the abdomen, and the fish turns over. Why?

Where are the kidneys? (Fig. 220.) Their ends unite close under the spinal column. The ureters, or tubes, leading from them, unite, and after passing a small urinary bladder, lead to a tiny urinary pore just behind the opening from the ovary. (Colored figure 4.)

The Circulation.—The fish, unlike other vertebrates, has its breathing organs and its heart in its head. The gills have already been described. The heart of an air-breathing vertebrate is near