The caudal fin is asymmetrical, extending along the dorsal and 

 ventral edges of the posterior end of the body. Observe the upward 

 bend of the vertebral column which occurs in the tail; it is this 

 character which marks the heterocercal type of tail. 



Eugaleus has a median ventral, or anal, fin a short distance anterior to the 

 caudal fin. 



The mouth is a broad transverse slit upon the ventral surface 

 of the head. The cartilaginous jaws can be seen and felt just within 

 the mouth. Both upper and lower jaws are armed with rows of flat, 

 sharply pointed teeth. Study their arrangement and approximate 

 number. Jaws of previously dissected specimens should be exam- 

 ined under a dissection miscroscope. The exact form and arrange- 

 ment of the functional teeth can then be ascertained easily, and an 

 examination of the inner surface of either jaw will disclose several 

 rows of developing teeth. As the young teeth develop they move, a 

 row at a time, into position on the edge of the jaw; the oldest teeth, 

 occupying the outer row, are shed at about the same time. 



The upper jaw is partly overhung by a lip-like fold of skin. At 

 each side of the mouth is a pocket, directed obliquely, having no 

 communication with the mouth. These labial pockets provide places 

 for the labial cartilages (which can be felt along the medial edges) 

 when the mouth is closed, and also afford freedom of motion to the 

 mandible. Cut along the inner edge of the labial pocket and ex- 

 pose the cartilages for examination. (The labial pocket of Euga- 

 leus is much smaller, and in front of the corner of the mouth rather 

 than lateral to it. The two cartilages are completely separated from 

 each other, the posterior one scarcely reaching the pocket.) 



In front of the mouth are the nostrils, their apertures apparently 

 divided by projecting flaps of the anterior margin. Explore the 

 cavity of the nostril with a probe to get a good idea of its size and 

 form. 



Between the pelvic fins is the cloaca, a large depression into 

 which open the alimentary canal, the excretory and genital ducts, 

 and the abdominal pores. The opening of the alimentary canal, the 

 anus, is at the anterior end of the cloaca. In preserved specimens 

 part of the intestine is frequently everted through the anus. A large 

 fleshy process, bearing a pore at its tip, projects from the dorsal wall 

 of the cloaca. In the male this is the urogenital papilla; in the 

 female the urinary papilla. In the female a genital pore, the open- 

 ing of the oviduct, is found on either side of the papilla. An 

 abdominal pore, leading into the abdominal cavity, is found on 

 each side of the cloaca at the posterior margin. These are frequently 

 closed in young specimens. 



The cloaca of Eugaleus has a comparatively small opening upon the ventral 

 surface, which must be enlarged before the parts described can be seen well. 



The laterally placed eyes are without lids; observe the consider- 

 able difference in the amount of curvature of the dorsal and ventral 

 margins of the eye. 



In Eugaleus there is a fold of skin stretched across the lower part of the 

 eye which serves as an eye-lid, and corresponds to the so-called "third eye-lid" 

 or nictitating membrane of other vertebrates. 



On each side of the neck are five vertical gill-clefts, each leading 

 into a large gill-pouch which communicates with the pharynx by an 

 internal opening. Pass a probe through a gill-cleft into the mouth. 



Back of each eye is a small aperture, the spiracle; explore this 

 cavity with a probe. The spiracle is to be considered a gill-cleft 

 moved forward upon the head and largely, though not entirely, de- 

 prived of its respiratory functions. 



In the center of the dorsal surface of the head, between the 



