354 



MANUAL OF ELEMENTARY ZOOLOGY 



narrows and loses its spiral valve, thus becoming the rectum, 

 this in turn ending in the wider cloaca, which receives the 

 urinary and generative ducts and opens by the vent. 

 There is no bladder. The liver is a very large organ, 

 consisting of long right and left lobes united in front and 

 slung by the falciform ligament from the anterior wall of 

 the peritoneal cavity. The gall bladder is embedded in 

 the front part of the left lobe of the liver, but usually a 

 part of it shows upon the surface. From it the bile duct 

 runs backwards to open into the intestine, lying in the 

 membrane or omentum which carries the hepatic artery 

 and portal vein. The pancreas lies 

 between the stomach and intestine ; 

 it is long and narrow and has in front 

 a rounded ventral lobe, from which 

 its duct passes to the ventral side of 

 the intestine. The rectal gland is 

 a small, cylindrical structure which 

 opens into the dorsal side of the 

 rectum by a duct. The spleen must 

 be mentioned here, although it has 

 no connection with the alimentary 

 canal. It is attached by membrane 

 to the hinder end of the stomach as 

 Diagram of a triangular lobe with a forward pro- 

 longation along the right side of the 

 pyloric division. 

 The kidneys of the dogfish are relatively longer than 

 those of the frog, but otherwise resemble them 

 Excretory and i n position and structure, lying above the 

 organs. abdominal cavity just outside the peritoneum, 



and consisting of numerous tubules, whose 

 nephrostomes in this case remain open. In the early 

 stages of development the tubules correspond with the 

 muscle segments, but later they become more numerous. 

 The kidneys have three sections, known as the fore, mid, and 

 hind kidneys, or pro-, meso-, and metanephros, 1 but the first 



1 The permanent meso- and metanephros of the dogfish correspond 

 only roughly with the regions to which the same names are given in the 

 embryos of higher vertebrates. For this reason the latter is sometimes 

 called the opisthonephros. 



Fig. 253 



spiral valve. — -After 

 T. J. Parker. 



