256 THE DOG-FISH 



Squeeze the head of a fresh specimen, so as to make the 

 gelatinous matter exude, and so render visible the position of 

 the openings 



Remove the skin from the' dorsal and ventral surfaces of the 

 head, an operation mvxsh facilitated by dipping the head in 

 hot water for a few moments : identify the masses of ampulla 

 and the nerves in connection with them, and trace the tubes 

 outwards and backwa/rds to their openings. Some of the tubes 

 which run along the dorsal surface of the skull, between the 

 cranium and the orbit, a/re some inches in length. 



Gut out a small piece of the mass of ampullce : put it on a 

 slide in a drop of water : separate the parts with needles : 

 cover, and examine under the microscope. Note the ampullce, 

 their internal divisions, the nerves supplying them, and the 



