CHORD ATA 317 



and the esophagus in front of stomach. Remove, open, and examine interior. 

 Figure differences in different portions. Look for parasites in the tract. 



2. Reproductive and Excretory Organs. Find the whitish testes or the yellow 

 or pinkish ovary (or ovaries). Do they possess ducts? Where is the outlet? 



Observe position and dimensions of the air-bladder (if present) ; pierce it and 

 discover dorsal to it the red kidneys. Number, shape, and dimensions of these? 

 Can you find their outlets? 



3. Pericardial Cavity and its Contents. 

 Shape and boundaries of the cavity. 



Heart: position; portions; ventricle (ventral) and auricle (more dorsal). 

 From the ventricle the whitish bulbus arteriosus passes forward and 

 narrows into the ventral aorta. Posterior to the heart is the thin-walled 

 sinus venosus which communicates with the auricle. 



[The teacher may supplement this work by a demonstration of the ventral 

 aorta with its branches passing to the gills, by means of a larger fish in which these 

 vessels have been injected with a colored mass. See appendix.] 



4. The Nervous System. Cut off the head and remove the muscles from the 

 back and top of the skull. Use a strong cartilage knife and gradually slice and 

 pick the bone until the cavity within is well uncovered. Note the loose tissues 

 covering the brain. Remove this with great care. 



Beginning in front, identify as you pass backward: olfactory lobes, tapering 

 toward the front and communicating with the nasal cavities; cerebrum, two oval 

 prominences meeting in the middle line; the two large, rounded optic lobes; the 

 cerebellum, a single median lobe; and the medulla oblongata, which tapers backward 

 into the spinal cord. Is there any real boundary between the spinal cord and the 

 medulla, or is the distinction arbitrary? What is the size of -the cord where it 

 emerges from the cranium? What is its position in relation to the vertebrae? 

 Have you found any nerves leaving the medulla or the cord? If so how many? 

 Are there any cavities in the brain lobes? 



5. The Eye. Remove the bone from above the eye and examine it in position. 

 How is the eye moved in life ? Can you discover any of the muscles effecting these 

 motions? How are they attached? What is the shape of the eye? Split it 

 open, and find the lens. Is the lens more or less nearly spherical than you expected ? 



6. The Skeleton. The general shape and character of the skull and its bones 

 may be seen by boiling the head of another fish and scraping and picking away the 

 flesh. The principal regions are the cranium or brain case, the opercular bones of 

 the gill covers, and the facial bones. Notice the loose way in which the lower jaw 

 is articulated. 



Boil a two inch block taken from the tail of the fish until it becomes tender. 

 Notice incidentally the shape of the individual myotomes or muscle segments as 

 they fall apart. Clean the vertebrae of flesh, and study the structure of one of 

 them. Note the centrum; the dorsal or neural arch and spine; the ventral or hamal 

 arch and spine. What is the shape of the centrum? What structures occupy 

 the arches? Prepare a trunk vertebra and compare in all respects with the caudal. 

 How are the ribs related to the vertebra? Can you find any evidence whether 

 they are homologous with the haemal processes ? 



Are there any bones connected with the fins? 



D. General Questions. What internal organs show segmentation? Do they 

 show it equally in all parts of the body? Do the internal organs show bilateral 



