8 



The muscular coat consists of an outer circular and an inner 

 longitudinal layer of muscle fibres. Separate the two layers from 

 each other and from the mucous coat; observe the network of 

 blood vessels between the longitudinal muscles and the mucosa. 



Open the pyloric end of the stomach, continuing the cut through 

 the pylorus into the intestine. Examine the coats as before, observ- 

 ing especially that an outer layer of longitudinal muscle fibres is 

 frequently developed, and that the pyloric valve is formed by an 

 increase in the thickness of the coat of circular fibres. 



Cut through the wall of the large intestine along the right side 

 from its anterior end to the rectum. Do not cut deeper than the 

 thickness of the wall. Corresponding to the external markings, the 

 mucous membrane projects internally in a spiral fold, known as 

 the spiral valve. Separate the wall of the intestine from the edge 

 of the spiral fold upon both sides of the longitudinal incision, ex- 

 posing a considerable surface of the valve. Wash well, and ob- 

 serve the character of the valve, the direction of the folds, and the 

 manner of the reversal of their direction which usually takes place 

 in the posterior half of the valve. 



Cut across the rectal gland at its middle. Observe the character 

 of its tissues, and then insert a bristle into the central cavity of the 

 gland and pass it into the rectum. Open the rectum and note the 

 point of communication of the two organs. 



URINARY AND REPRODUCTIVE ORGANS. The kidneys (mesonephri, 

 Wolffian bodies}, are slender bodies extending along the entire 

 length of the dorsal wall of the abdomen. The posterior moiety of 

 each is thicker and wider than the anterior, which appears to have 

 largely lost the functions of excretion in adult dogfish. Notice the 

 position of the kidneys outside the peritoneum. 



THE MALE.- The testes are white bodies lying to the right and 

 left of the oesophagus, dorsal to the anterior portion of the liver. 

 Each is suspended by a fold of the peritoneum, the mesorchium. 

 (The testes of Galeus are long bodies attached to the sides of the 

 mesentery. ) 



Showing through the peritoneum, a much convoluted, white tube 

 can be seen on the ventral surface of the kidney. This is the 

 mesonephric or Wolffian duct. In young specimens it may be 

 nearly straight, lying near the medial border of the kidney. In adult 

 ^specimens it can be followed forward as far as the anterior end of 

 the testis. While the Wolffian duct is the duct of the kidney, and is 

 joined by tubules of the anterior part of the kidney, it is so modified 

 in the male that its principal function is to serve as the duct of the 

 testis, a vas defere.ns. The collecting tubules of the posterior part 

 of the kidney join to form a urinary duct which is independent of 

 the Wolffian duct. The posterior end of the Wolffian duct is straight 

 and considerably expanded, forming a large seminal vesicle. The 

 duct becomes more and more closely convoluted as it passes for- 

 ward, and the kidney tissue overlying it diminishes. At the an- 

 terior end of the mesonephros the Wolffian duct forms a mass of 

 tubules, the epididymis. Very small tubules, the vasa efferentia, 

 pass from the anterior end of the testis to the epididymis. These 

 are difficult for the student to distinguish. 



Cut through the peritoneum along the outer side of one kidney. 

 Then strip the peritoneum toward the inner border of the kidney. 

 The urinary duct will usually be closely attached to the peritoneum 

 and parallel with the Wolffian duct, but nearer the midline of the 

 body. The urinary duct can be separated from the peritoneum by 



