CHORD ATA 3 I 7 



identify all the external openings. How would you describe the general shape of 

 the body? What are the external evidences of segmentation? 



The A ppendages. — How many paired ? Unpaired ? Locate : the dorsal, caudal, 

 anal, the pectoral, and the pelvic or ventral. Does the skin of the body extend 

 over the fins? What seems to be the nature of the fin rays? Number? Are the 

 upper and lower lobes of the caudal fin equal or unequal? 



The Covering. — Does the specimen possess scales? Is there any regularity in 

 their arrangement? Is this constant among several specimens? Is it the same 

 in different species? Are any parts of the body free of scales? Are the scales 

 covered with skin? What is the shape and nature of the free margin of the scales? 

 Examine with a hand lens or low power of microscope. Is there any color? How 

 does this appear under the microscope? Do you distinguish a line {lateral line) 

 along one of the rows of scales on the side of the body? Examine one of these 

 scales under the microscope. How does it differ from the others? How many 

 rows of scales above the lateral line? Below? 



The Head. — What goes to make up the head of the fish? Note position, shape 

 and size of mouth. Find the bony framework: upper jaw {premaxillaries in front 

 articulating with maxillaries behind); lower jaw (dentaries). Are both jaws 

 movable? Locate all the bones which bear teeth? How are teeth arranged? 

 Is there a tongue? Do the nostrils communicate with the mouth cavity? 

 Eyes: number, position, coverings (lids?), iris, pupil. 

 Are there any "ears?" Evidences? 



Gills and Gill-coverings. — How many bones in the gill cover {operculum) ? 

 Describe the structure at its inner, lower margin. How wide is the isthmus 

 between the right and left gill-openings ? Identify and number the gill arches, 

 which bear the reddish gill-filaments, and the gill slits between. With what do the 

 passages between the gill arches communicate? Determine by extending a probe 

 into mouth. How does the inner or pharyngeal side of the gill arches differ from 

 that which bears the filaments? Examine the gills for parasites: 



C. Internal Structure. — With forceps and sharp scalpel remove a strip of skin 

 an inch wide from one side of the fish, from the belly to the dorsal fin. Note the 

 muscular segments {myotomes). Is the line separating two of these a straight line? 

 In what direction do the muscle fibres run? 



With scissors cut the body wall along the middle line of the belly from just in 

 front of the anus to the isthmus. Be very careful not to injure any of the organs 

 within the ccelom. A portion of the side muscles may be removed on one side 

 or cuts may be mad© perpendicular to the first so that the sides may be more readily 

 opened. Notice the lining of the body cavity {peritoneum). Color? How is 

 the heart separated from the abdominal cavity? {False diaphragm.) Sketch 

 the cavities thus laid open and represent the organs as they appear before dis- 

 turbing them. Has the liver lobes? 



Examine more in detail, turning liver to one side. 



I. Digestive Organs. — Extend probe through the mouth into stomach, and 

 locate: esophagus; stomach, form and position; intestine, its point of origin, course 

 and outlet. About the junction of stomach and small intestine look for finger-like 

 projections from the surface of the gut {pyloric cceca). If present, cut one: is it 

 solid or hollow? Examine the membrane {mesentery) which holds the intestine 

 in place. To what part of the body wall is it attached? The spleen, a dark-red, 

 ductless gland, occurs close to the intestine. Cut intestine an inch from the anus 



