314 ZOOLOGY. 



that the sides may be more readily opened. Notice the lining of the body 

 cavity (peritoneum'}. Color? How is the heart separated from the ab- 

 dominal cavity? (False diaphragm.} Sketch the cavities thus laid open 

 and represent the organs as they appear before disturbing them. Has the 

 liver lobes? 



Examine more in detail, turning liver to one side. 



1. Digestive Organs. Extend probe through the mouth into stomach, 

 and locate: oesophagus; 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 area). 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 and the 

 oesophagus 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 dimen- 

 sions of these? Can you find their outlets? 



3. Pericardia! 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. Back of the heart is 



the thin-walled sinus venosus which communicates with the auricle. 



[The teacher should 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 dis- 

 tinction 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? 



