CHORDATA. 313 



The Topography of the Body. Note the symmetry; indicate the degree 

 of differentiation of anterior and posterior ends, and of dorsal and ventral 

 surfaces, as shown by the shape, special organs, etc. What structures 

 appear paired? To what degree are head, trunk, and tail clearly distin- 

 guishable? Locate and identify all the external openings. How would 

 you describe the general shape of the body? What are the external evi- 

 dences of segmentation? 



The Appendages. 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 regu- 

 larity 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 posi- 

 tion, shape and size of mouth. Find the bony frame-work: upper jaw 

 (prcmaxillaries in front, articulating with maxillarics 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 (opercu- 

 lum) ? Describe the structure at its inner, lower margin. How wide is 

 the isthmus between the right and left gill-openings? Identify and num- 

 ber 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 made perpendicular to the first so 



