THE CATFISH. 103 



anterior border of eye; trunk, distance from the posterior angle of the 

 operculum to a mid-lateral point directly above the anus; tail, the 

 distance from the latter point to the base of the caudal fin; depth, the 

 greatest vertical diameter; width, the greatest diameter from side to 

 side. How many times is the width contained in the total length ? 

 The region between the anal and the caudal fins is the caudal 

 peduncle. 



Exercise i. Make an outline drawing of the left side of the fish, natural 

 size if the specimen is not over five inches long. Represent the 

 mouth open slightly and the fins extended in the normal position when 

 swimming. Give attention to the actual number of rays in the fins. 

 Label all the parts. 



Exercise 2. Make an outline sketch of the ventral surface of the head and a 

 small portion of the trunk. 



Exercise 3. Remove the operculum on the left side and sketch the head and 

 gills. 



Exercise 4. Split the mouth from the corners to the upper angle of the 

 operculum in order to get a better view of the interior. Make one 

 diagram of the roof of the mouth and one of the fioor. 



Exercise 5. Remove and draw, on an enlarged scale, the spine of the 

 dorsal fin and one of the longer jointed fin rays. 



INTERNAL ANATOMY. With a fresh specimen, if obtainable, or a 

 preserved one from which the formaldehyde has been thoroughly 

 rinsed, we will proceed to a study of the internal organs. 



Technical Note. With the scissors make an incision in the mid-ventral 

 line of the body at a point just ahead of the anus. From here cut 

 transversely right and left as far as the thin ventral wall extends, 

 thence forward on each side to the shoulder girdle. Turn forward the 

 flap thus partially cut free, or remove it entirely by cutting across 

 back of the shoulder girdle. 



