A MANUAL OF ZOOLOGY , 47 



Remove the skin from the whole side of the fish by 

 cutting along th^ back near the dorsal fins, taking care 

 not to injure the musculature beneath. Roll the sfcin 

 lengthwise to see the arrangement of the rows of scales 

 in that direction, and roll it crosswise to see the arrange- 

 ment of the scales and the epidermis. Look at the lateral 

 line from the inside of the skin with a hand lens. Is there 

 any indication of a lateral line on the musculature? Look 

 on the inside of the skin and on the body under the skin 

 with a lens for pigment cells.. In what are they situated? 

 Make a drawing of the muscle arrangement on the side 

 of the fish. Carefully pick and scrape the muscles away 

 so as to expose the skeleton. Take out a. few vertebrae 

 and attached bones over the visceral cavity. Does the fish 

 have ribs? What peculiarity is there in the articulation 

 of the vertebrae? The largest and ventral part of a verte- 

 bra is called the centrum. Is it hollow? Notice the 

 canal traversed by the spinal cord. This is called the 

 neural cavity, and the bones forming it the neural arch. 

 The neural spine projects dorsally from the neural arch. 

 Do the neural spines connect directly with the dorsal 

 fins? Sketch a dorsal vertebra and the connecting bones 

 side view, also end view. Take out a few vertebrae from 

 near the tall. How do they comipare with the dorsal ver- 

 tebrae? On the ventral portion note the haemal' arch, 

 for the passage of the dorsal aorta, and the ventral spine 

 projecting ventrally. Observe how the blood vessels are 

 given off. Sketch : a caudal vertebra from the side, also 

 from the end. 



Dissect out the brain with much care by commencing 

 on th'e dorsal anterior portion. Note the nasal sacs and 

 the nerves leading to them. Trace the two olfactory nerves^ 

 back to the- two ^olfactory lobes. How do they compare 

 with those of the dog-fish? Back of the small olfactory 

 lobes find the cerebral hemispheres constituting the cere-> 

 brum. Observe the' immense ' advance of the cerebrum 

 here over the dog-flsh. Back of ■ the cerebrum note the 

 two round, paifed optic lobe* constituting the largest and 

 ihe widest part of the brain. Back of these is thecerebel- 

 lum; Beneath this cerebellum and extending backward is 

 the rhedullti:oblengata. From the undei* side of the 'brain 



